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ELECTRICITY, MAGNETISM, 


AND 

ELECTRIC TELEGRAPHY 


A PRACTICAL GUIDE AND HAND-BOOK 

OF 


GENERAL INFORMATION FOR ELECTRICAL STUDENTS, 
OPERATORS, AND INSPECTORS. 


BY 

THOMAS D. LOCKWOOD. 

w 


THIRD EDITION. 

■y » 

D > 


$Uur 'Hot h : 

Oc VAN NOSTRAND COMPANY, 

23 Murray Street & 27 Warren Street. 


1 890. 




T‘Km-5 
, L&- 

1890 


Copyrighted, 1883, 

By D. VAX NOSTRAXD. 

GiFT 

MISS E. M KITTREDGE 
JAN* 22, 1*40 













INTRODUCTION. 


Electricity is pre-eminently a science of the nine- 
teen tli century. 

We cannot even at this late day say that we know 
what electricity is ; and within a comparatively recent 
period even its manifestations and phenomena were fa¬ 
miliar to a relatively small class, composed chieliy of 
college professors and scientific lecturers. 

Few of the class which was entrusted with the man¬ 
agement of its practical applications—viz., telegraphers 
and electro metallurgists—had any scientific knowledge 
of its laws, or, in fact, anything but a mechanical and 
empirical knowledge of the manipulation of the tele¬ 
graph instrument and the electrolyzing battery. 

This state of things lias, however, passed away, and 
electricity has become the favorite, most promising, and 
most important scientific study of that section of the 
human race which, under the title of inventor, aspires 
to achieve fame or fortune, or both, by the work of its 
own brains. 

During the last decade we have seen such wonderful 
developments in electricity and electro-magnetism that 
while on the one hand we can scarcely conceive of any¬ 
thing which cannot be done by these agencies, on the 
other hand we are almost compelled to believe that 
there is little more left for electricity to achieve. 

It is true that for many of the greatest discoveries 



4 


INTRODUCTION. 


and inventions wliicli have been made we are indebted 
to persons who have not been practical electricians, but 
it is also true that it is to the practical electrician we 
turn when these discoveries are to be utilized ; and it is 
to be regretted that among the thousands of our tele¬ 
graphers and telephonists so few are to be found capa¬ 
ble of assuming an important trust, and of practically 
and ably filling important positions in the many appli¬ 
cations of electricity. 

A general knowledge of the theory and practice of 
electricity and magnetism is, then, a most desirable and 
valuable acquirement for all who are in any way, or 
who intend to be, connected with the practical applica¬ 
tion of either science. 

And this desirability, and the knowledge that but few 
of the many books written upon the subject are fitted 
for the self-helper, who has to struggle against many 
difficulties, notably that of neglected early education, 
forms the excuse of the author for inflicting another 
book upon the electrical public. 

Imperfect as this volume is in many ways, such a one 
would have been a great help to the author had he in 
his earlier years had the fortune to stumble across it, 
and it is his earnest hope that its contents will in some 
measure aid those for whom it is written—those who 
desire to obtain a knowledge of electricity and magnet¬ 
ism and their possibilities, but who are unable to obtain 
the advantages of a college or institution course—and 
enable them to answer for themselves the innumerable 
questions which constantly force themselves upon the 
thinking mind when daily occupied in the utilization 
of these mysterious agencies. If the readers of this 
work learn but one tithe as much of the various sub- 


INTRODUCTION. 


5 


jects treated of as the author has while working upon 
it, they will be benefited, and will perhaps be more 
ready to digest the more solid contents of such standard 
books as Culley’s “ Hand-book of Practical Telegraphy ” 
and Fleeming Jenkin’s “Electricity and Magnetism.” 

The author has endeavored to put the information in 
as lucid and concise form as is consistent with accuracy, 
and to combine brevity with completeness. How he 
has succeeded is for others to judge. A liberal use 
has been made of the electrical text-books, and of the 
literature relating to kindred subjects, also of the cur¬ 
rent electrical journals of the day ; and valuable infor¬ 
mation has especially been obtained from the well- 
known ‘ ‘ Modern Practice of the Electric Telegraph ’ ’ by 
Mr. Pope; Culley’s “Hand-book of the Electric Tele¬ 
graph” ; Prescott’s “ Electricity and the Electric Tele¬ 
graph” ; Preece and Sivewright’s “Telegraphy” ; and 
“Elementary Lessons in Electricity and Magnetism,” 
by Silvanus P. Thompson. 

The acknowledgments of the author are also due to 
his friend Frank L. Pope for his constant advice and 
encouragement during the preparation of the work. 


t 



CONTENTS. 


CHAPTER I. 

Electricity generated by Friction,.9 

CHAPTER II. 

Voltaic Electricity,.22 

CHAPTER III. 

Thermo-Electricity,.36 

CHAPTER IV. 

Earth-Currents and Earth-Batteries,.41 

CHAPTER V. 

Magnetism—Electro-Magnetism and Electro-Magnets, . . 43 

CHAPTER VI. 

Magneto-Electricity, and Magneto and Dynamo-Electric Ma¬ 


chines, .59 

CHAPTER VII. 

Induction-Coils and Condensers,.80 

CHAPTER VIII. 


Definitions of Electrical Properties, Terms, and Units, • • 89 

CHAPTER IX. 

Electrical Measurements, ........ 98 

CHAPTER X. 

Principles of Telegraphy exemplified in Different Systems, . 130 

CHAPTER XI. 

Voltaic Circuits,.. 142 

7 





8 


CONTEXTS. 


CHAPTER XII. page 

Line Construction,.. . .153 

CHAPTER XIII. 

Subterranean and Submarine Conductors, .... 184 

CHAPTER XIV. 

Office-Wires, and Fittings and Instruments, .... 192 

CHAPTER XV. 

Adjustment and Care of Telegraph Instruments, . . . 222 

CHAPTER XVI. 

Circuit Faults and tlieir Localization, .231 

CHAPTER XVII. 

Multiple Telegraphs,.242 

CHAPTER XVIII. 

Miscellaneous Applications of Electricity—Electric Lighting, . 266 

CHAPTER XIX. 

Electro-Metallurgy,.281 

CHAPTER XX. 

Electric Bells, . . . .'.286 

CHAPTER XXI. 

The Telephone,.299 

CHAPTER XXII. 

Electro-Therapeutics,.318 

CHAPTER XXIII. 

Other Applications of Electricity:—Electric Clocks—Time-Balls 
—Alarms—Blasting—Transmission of Power—Electrical 
Storage,.323 

CHAPTER XXIV. 

Odds and Ends,.351 








- 4 **- 


CHAPTER I. 

ELECTRICITY GENERATED BY FRICTION. 

» 

1. What is electricity i 

Electricity is one of the peculiar forces of nature; 
it is as universal in its effects as its kindred forces, light 
and heat, and is in many respects analogous to them. 
It has been common to speak and write of electricity as 
if it were a fluid, capable of flowing as a current. It 
is, however, now usually considered by scientists to be 
simply a particular form of energy,* which causes the 
infinitesimal particles of matter to alter their positions 
in regard to one another. 

2. From whence does electricity derive its name i 

It was observed in ancient times that when amber f 
was rubbed it acquired a power of attracting and re¬ 
pelling light bodies, such as hair and feathers. This 
power afterwards came to be called electricity, from 
4 ‘ electron , 5 ’ the Greek word for amber. 

3. Why has it become customary to speak of electricity as if 
it ivere a fluid, and consequently subject to the laics of fluids f 

Because for many years it was in fact thought to 
be a fluid. The fluid theory was first propounded by 

* Energy in a mechanical sense may be defined as capacity for performing work 
or for moving against resistance. 

+ Amber is a resin of yellowish color resembling copal, found as a fossil. It takes 
a fine polish and is used for ornaments and also as a basis for a superior quality of 
varnish. 


9 
















10 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


Dii Fay, of France, who supposed that there were two 
electric fluids, naturally commingled and neutralized, 
which universally pervaded all matter. Dr. Benjamin 
Franklin proposed a second hypothesis, ascribing all 
observed electrical effects to one fluid, which, as in the 
former case, was supposed to pervade all bodies. Ac¬ 
cording to Franklin’s theory, it was supposed that the 
electrical equilibrium or balance constituting the natural 
state of matter was disturbed by friction, and that one 
of the two bodies brought near to each other, was, so 
to speak, over-saturated with electricity, while the other 
was left under-saturated. This also explains the origin 
of the terms plus and minus as applied to opposite 
electrical states or conditions. As the terms which have 
come to be adopted in speaking of electricity and its 
properties are nearly all based on the foregoing tlieo 
ries, and have in this manner become familiar to men 
of science everywhere, it has by common consent been 
considered unwise as well as unnecessary to change 
them. 

4. What is the simplest method of producing electricity i 

By rubbing together two suitable substances, such, 
for example, as a tube or rod of glass and a woollen 
cloth. Electricity so produced is called frictional elec¬ 
tricity. 

5. Is not electricity produced in different states or conditions f 

Yes. Certain substances, such as sealing-wax and 

resin, when rubbed by a woollen cloth, exhibit wliat is 
sometimes called resinous electricity; while glass or 
other vitreous bodies, when rubbed with the same cloth, 
exhibit what is called vitreous electricity. These names 
are, however, somewhat unsuitable, as they imply that 
the same substances always produce the same kind of 
electricity, irrespective of conditions ; whereas a tube of 
glass, when rubbed by the fur of a cat, produces the same 
kind of electricity as sealing-wax. The terms positive 
and negative are less objectionable, and are still very 
generally employed. 


ELECTRICITY GENERATED BY FRICTION. 11 

We may, therefore, call the electricity produced by 
rubbing glass with a woollen cloth positive, and denote 
it, for the sake of brevity, by the sign plus, or + ; and 
that produced on a stick of sealing-wax, when rubbed, 
negative, and denote it by the sign minus, or —. 
These terms, however, must not be understood to indi¬ 
cate that one electricity is more powerful or potent than 
the other; they are purely arbitrary, and merely used 
for the sake of distinction, to denote that the two elec¬ 
trical states are opposite in character. Both kinds of 
. electricity are always produced at the same time and in 
equal quantities, one of the bodies rubbed exhibiting 
plus and the other minus electricity. 

6. What is an electrical conductor f 

Conductors are those bodies and substances which 
permit electricity to freely diffuse itself through them. 
All the known metals are good conductors. Many 
non-metallic substances are also conductors. The inhe¬ 
rent conducting power of bodies depends largely ujDon 
conditions ; for instance, ordinary water when in liquid, 
form is a conductor, but when frozen becomes a non¬ 
conductor. Iron, when cold, is a good conductor ; when 
hot, a very poor one. 

7. What is an insulator , or non-conductor f 

Bodies which offer very great resistance to the pas¬ 
sage of electricity, such as dry air, paraffine, gutta¬ 
percha, india-rubber, and glass, are called non conduc¬ 
tors, or insulators, from insvla , an island. There is no 
absolute distinction between insulators and conduc¬ 
tors. The difference is in degree only, all bodies be¬ 
ing, strictly speaking, conductors in a greater or less 
degree, the worst conductors being the best insulators. 
Hence a list of conductors, arranged in the order of their 
conducting power, becomes, if read backward, a list of 
insulators, and in the middle of the list the conductors 
and insulators merge insensibly into each other. 


12 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


8. Define the terms “ electric ” and “ non-electricwhich are 
sometimes applied to substances. 

It was formerly considered that insulators were the 
only bodies upon which electricity could be excited, 
hence they were also denominated electrics ; while the 
conductors, such as the metals, were called non-electrics. 
This supposition was, however, an erroneous one, as, 
when properly insulated, the most perfect conductors 
can be electrified. The distinction between electrics and 
non-electrics is, therefore, no longer admissible, although 
the terms are still frequently used in works on electri¬ 
city. 



9. What is an electroscope f 

An instrument for indicating the presence and char¬ 
acter of electricity. A gold leaf electroscope consists 

of a glass vessel, B, into 
which is inserted a metallic 
rod terminating in two 
gold leaves, n, and sur¬ 
mounted by a metallic 
plate or ball, C. If the 
plate is touched by an 
electrified body, A, the ex¬ 
citement passes down to 
the leaves and causes them 
to repel each other, or to 
diverge. An instrument 
provided with means of 
measuring the amount of 
divergence, and thereby measuring the amount of elec¬ 
tricity present, is called an electrometer . 


Fig. 1.—The Electroscope. 


10. What is an electrical machine f 

It is an apparatus for obtaining large quantities of 
electricity, usually by the friction of an extended sur¬ 
face of some suitable non-conductor, such as glass or 
hard rubber. 

In order that glass may be conveniently subjected to 
friction for the development of electricity, it is formed 
















ELECTRICITY GENERATED BY FRICTION 


13 


into a circular plate, P 5 mounted on an axis supported 
on a wooden frame, O, and revolved by a crank, M, while 
cushions or rubbers, F, press against its surface. To 
equalize the pressure of the rubbers they are placed at 
the top and bottom, and on both sides, of the glass. 
In front of the plate are two rods of metal, C, supported 
by glass legs. These are called the prime conductors, 



Fig. 2.—The Electrical Machine. 

and are provided with branches, which are studded with 
sharp points and bent round the glass plate. 

When the plate is revolved by means of the crank, by 
reason of the friction against the cushions it becomes 
positively electrified ; negative or minus electricity be¬ 
ing at the same time produced in the rubber. When 
the plus electricity, carried round by the rotation of the 

































































































14 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

plate, arrives opposite the points of the prime conductor, 
it acts inductively thereon, repelling its plus electricity 
to the distant end and attracting minus electricity to 
the end nearest the machine. The points then discharge 
the minus electricity so accumulated towards the plus 
charge on the revolving plate, which is thus neutralized, 
and the neutralized portion of the plate arrives at the 
rubber in a neutral state and ready once more to be 
excited. If now any electrically neutral substance be 
brought near to the distant end of the prime conductor, 
minus electricity will be abstracted from it and will 
pass along the conductor to keep up’ the supply neces¬ 
sary for a continuous neutralization of the excited plate; 
hence the prime conductor, and any conductor attached 
or brought near thereto, will acquire a surplus of plus 
electricity, or become charged, and this charge may be 
conducted away or collected in Leyden jars at will for 
experimental purposes. 

If it is desirable that the minus electricity be also col¬ 
lected, the rubber is supported upon a non-conducting 
stand and provided at the back with a metallic knob. 

But generally, the negative or minus electricity is al¬ 
lowed to pass to earth by connecting the rubbers, by 
means of a chain or wire, D, with the earth. 

In charging a Leyden jar, if the rubbers are connected 
to earth, the outside of the jar must also be connected 
with the earth ; but if the outside of the jar and the 
rubbers be connected together it is not essential that 
either should be attached to earth. 

Another common form of the electrical machine is the 
cylinder. The chief distinction between this and the 
plate machine lies in the use of a cylinder of glass in¬ 
stead of a plate. 

11. What is an electvopliorus i 

It is an instrument, invented by Volta, which is an 
exceedingly convenient source of electricity when re¬ 
quired in comparatively small quantities. It consists of 
three essential elements: 1st. A cake, B, of some resinous 


ELECTRICITY GENERATED BY FRICTION. 


15 


material easily excited by friction. 2d. A conducting- 
plate, whicli is a metallic dish into which the resinous 
composition is poured, and which is connected to earth. 
3d. A disc of metal, or of wood covered with tin-foil, A, 
and provided with an insulating handle. 

It is very convenient to so arrange the electrophorus 
that the cover, when placed on the resinous plate, comes 
into metallic connection with the metal dish below, and 
thereby, of course, with the earth. The resinous cake is 
excited negatively by rubbing, and the metal plate laid 



Fig. 3.—The Electrophorus. 


upon it ; on lifting it away it is found to be positively 
electrified and will give a spark. It may then be re¬ 
placed on the lower plate and the process indefinitely 
repeated. 

The upper plate does not receive its charge direct from 
the excited resin, but by induction, the negative charge 
on the resin attracting the positive and repelling the 
negative electricity of the upper plate which, by means 
of the metal connection with the lower plate or by the 
touch of the finger as in the figure, escapes to earth. 
Instead of pouring a resinous composition into the 
















16 ELECTRICITY, MAGNETISM, AND TELEGRAPHY'. 

dish, a flat piece of vulcanite may be fixed therein to 
subserve the same purpose. 

12. Have machines for furnishing large quantities of electri¬ 
city been constructed on the principle of the electrophorus i 

Yes, such machines have been constructed by several 
physicists ; and one—that of Holtz—lias come into very 
general use. In it, as in other machines of this class, a 
small initial charge is given to a piece of varnished paper 
fixed on a stationary portion of the machine. 

This initial charge acts inductively and develops other 
charges, which are conveyed by a rotating glass disc to 
some other part of the machine, where they may either 
increase by accumulative action the initial charge or 
furnish the supply of electricity to a suitable collector; 
or the machine may be caused to perform both functions, 
much upon the same principle as that of the dynamo- 
electric machine. (See chapter vi.) 

Like the Gramme and other continuous-current ma¬ 
chines, it, too, is reversible ; and if a continuous supply 
of both plus and minus electricities be supplied simul¬ 
taneously to the opposite extremes of the machine, the 
movable parts of the machine will rotate. 

A Holtz machine may be made to furnish a continuous 
current, the strength of which is dependent upon the 
rate at which the movable part is rotated, becoming 
greater when the rotation increases in speed. 

13. What is the meaning of the words “static ” and “ dyna¬ 
mic ” when applied to electricity i 

They are derived from the Greek. The word 
“ static” conveys the idea of force at rest, and “dy¬ 
namic” the idea of action or of force due to motion. 
Electricity developed by friction is often called “stat¬ 
ical,” because it tends to remain quiescent on the bodies 
whereon it is excited, or in fact wherever it is placed. 

The word static, or statical, refers to the electrical 
condition of bodies whereon electricity remains station- 
ary. For instance, a Leyden jar may be charged, and 
remain charged without requiring a continual supply to 


ELECTRICITY GENERATED BY FRICTION. 


17 


be poured in; lienee the electricity it is charged with 
is called statical, or reposing, electricity. On the other 
hand, voltaic electricity is frequently styled dynamical , 
because the excitement arises in a constant stream, and 
can hardly be said to exist if it is not continually 
evolved, and in that condition it exercises or performs 
work; and statical electricity becomes transformed to 
dynamical when in the act of discharge, or when pass¬ 
ing from one body to another. 


14. What is a Leyden jar , and whence does it derive 
its name i 

It is a device for the accumulation of elec- 
tricity, and, described as simply as possible, 
consists of a glass jar coated both inside and 
out with tin-foil, except a few inches at the 
top. Through the cork or insulating cover is 
* passed a brass rod with a knob on the end, 
which is in electrical communication with the 

Leyden Jar. j[ nner coatings. 

It was discovered in November, 1745, by Kleist, a 
German ecclesiastic. The Leyden philosophers were 
the first to state the conditions necessary for its suc¬ 




cess, and hence it receiv¬ 
ed the name Leyden jar. 
The jar is charged by 
bringing the knob near 
to the prime conductor 
of the electrical machine, 
while the outer coating 
is usually in electrical 
communication with the 
earth. When the knob 
is brought into connec¬ 
tion with the outside 
coating of the jar a 
flash of intense brightness, 
port, immediately ensues, 
discharged. 


Fig. 5.— Discharge of a Leyden Jar. 

accompanied by a loud re- 
and the jar is said to be 












18 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

15. What does the term “ dielectric ” imply f 

The insulating substance which separates two con- 
ducting surfaces, and thereby enables them to sustain 
opposite electrical states, was by Faraday called a di¬ 
electric. 

The sheets of paraffined paper between the tin-foil 
sheets of a condenser, constitute a familiar example of 
a dielectric. All insulators are dielectrics, but the best 
insulators are not always the best dielectrics. 

The glass jar between the inside and outside coatings 
of tin-foil is, in a Leyden jar, the dielectric. 

16. What is an electric battery f 

When a great amount of surface is needed to store a 
considerable quantity of electricity, a number of jars 
are set in a box lined with tin foil so as to connect all 
the outer coatings together. Their inner coatings are 
also connected by conductors joining all the knobs to 
one central knob. This constitutes an electric battery . 
It is charged and discharged like a single jar, and its 
effect is much the same as would follow from one large 
jar whose extent of coating was equal to the sum of 
those which constitute the battery. 

17. Does static electricity reside at the surface , or throughout 
the substance of bodies i 

Electricity at rest, resides on the surface only of con¬ 
ductors. This may be proved by enclosing an electri¬ 
fied metallic sphere in two tight-fitting, lion-electrified 
hemispheres. If the hemispheres are quickly removed 
and presented to an electroscope they will be found to 
be electrified, while the sphere itself lias lost its elec¬ 
tricity. 

18. What may ice understand by the word “ induction" % 

It is the name given to electrical or magnetic effects 

produced in bodies to which the exciting force is not 
directly applied, and may for general purposes be di¬ 
vided into the following heads: 1st. Electrostatic or 
static induction is the influence which an electrified 
body has on all conducting bodies in its immediate 


ELECTRICITY GENERATED BY FRICTION. 19 

vicinity, even tliougli it has not touched them, causing 
them to exhibit signs of electrification. It is similar to 
the power exerted by a magnet on pieces of iron which 
may be near it. 2d. Dynamic or voltaic induction is 
the power which a galvanic current lias, when flowing in 
a conductor, of inducing currents in neighboring con¬ 
ductors. 

For example, should two wires be placed near each 
other, parallel but not touching, one connected with a 
battery by means of a circuit-closing key, the other to a 
sensitive galvanometer, it would be seen that whenever 
the circuit was closed by the key on the first wire, and a 
current thereby caused to pass through it, the galvano¬ 
meter attached to the second wire is deflected by a cur¬ 
rent flowing in the opposite direction to the battery 
current. 

The battery current is called the inducing or primary 
current; the current that deflects the galvanometer the 
induced or secondary current. The induced current 
lasts but for an instant. When, however, contact is 
once more broken the needle is again deflected, but 
this time the induced current flows in the same direction 
as the primary current, and is, like the former current, 
instantaneous. 

3d. Electro-magnetic induction is the power which an 
electric current, traversing a conductor, has upon non- 
magnetized iron, which, under certain conditions, may 
by its influence become converted into a magnet. 

This power is the basis of one of the most universally 
useful applications of electricity—namely, the electro - 
magnet. 

4th. Magneto-electric induction is the converse of 
electro-magnetic induction—the one is the induction of 
magnetism by an electric current, the other the induc¬ 
tion of an electric current by a magnet. 

The name is popularly applied to the production of 
electric currents through the movement of a conductor 
through a magnetic field, or the movement of a per- 


20 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

manent magnet in the immediate proximity of a con¬ 
ductor. 

5th. Magnetic induction is that power by which 
pieces of iron, or other substances capable of acquiring 
magnetism, become temporary magnets when placed 
near a magnet, even when they do not touch it. 

19. Has f rictional electricity been put to any practical appli• 
cation f 

Yes ; but not to any such extent as voltaic electricity. 
It has been somewhat extensively used in chemistry, 
and has been applied with considerable success for ignit¬ 
ing gas-jets and fuses for blasting. 

20. Is friction the only method of producing electricity t 

No ; there are many other methods of evolving it, but¬ 
ch emical action is by far the most important source of 
electricity, and is the only one that has had a universal 
practical application in telegraphy. More recently, how¬ 
ever, magneto-electricity lias attracted much attention, 
and has been considerably applied to telegraphy, elec¬ 
tro-metallurgy, and to the production of the electric 
light. 

The production of electricity by heat constitutes a 
separate branch of the subject—namely, thermo-electri¬ 
city , which will be hereafter considered. 

21. What is the most familiar natural form of electricity f 

Atmospheric electricity, in the form of the thunder¬ 
cloud with its resultant phenomena of thunder and 
lightning. The resemblance between lightning and the 
electric spark was noticed at an early date. Dr. Wall 
pointed this out in 1708, and it has also been noted by 
other philosophers; but to Benjamin Franklin is due the 
credit of proving their identity by actual experiment, 
in drawing lightning from a cloud by the instrumen¬ 
tality of a kite, and by performing electrical experi¬ 
ments with it. 

22. Had this discovery any usefid result i 

Yes, it has resulted in the general application of the 
lightning-rod as a method of defending buildings from 


ELECTRICITY GENERATED BY FRICTION. 


21 


the effects of atmospheric electricity. The lightning- 
rod is constructed on the principle that electricity uni¬ 
formly chooses the best conductor within its reach, and 
consists of a rod of iron or copper, from half an inch to 
an inch in diameter, extending a considerable distance 
above the highest point of the building, and continued 
down the wall to terminate in the ground. 

23 . What is the most common defect in the construction of 
lightning-rods i 

They are frequently set up with a very imperfect con¬ 
nection with the ground, hence the lightning, finding a 
better conducting medium through some portion of the 
building, takes that path, often with most destructive re¬ 
sults. The rod ought always to terminate in a conside¬ 
rable depth of moist earth, and for this reason none 
should engage in the business of constructing and erect¬ 
ing lightning-rods unless they are well acquainted with 
the principles of electricity. 


CHAPTER II. 


VOLTAIC ELECTRICITY. 

24 . What is voltaic or galvanic electricity f 

These names are given to electricity evolved by che¬ 
mical action. They are so called in honor of Galvani 
and Volta, two Italian philosophers who made the ear¬ 
liest discoveries in this branch of the subject. As pre¬ 
viously stated, this is sometimes called dynamical or 
current electricity, because it is electricity in motion. 

25 . What are the chief points of difference between voltaic and 
f rictional electricity i 

While voltaic electricity resembles the electricity gen¬ 
erated by the frictional machine in a sufficient degree 
to establish its identity therewith, its characteristics, 
nevertheless, differ materially. Electricity evolved by a 
battery is of low potential or tension, and is, therefore, 
comparatively easily insulated. It flows in a steady and 
continuous current, and is produced in great quantities. 
On the other hand, in the frictional form, electricity is 
extremely energetic, being able to transfer itself violently 
(and with the evolution of light and heat) through and 
over insulating substances. It is, therefore, said to be 
of high potential. 

Voltaic electricity is capable of producing the most 
extensive magnetic and chemical effects, and is con¬ 
sequently by far the most important form and the most 
valuable agent in the arts and sciences. To sum up: 
frictional electricity has high potential, but is produced 
in small quantity, while current electricity has an ex¬ 
tremely low potential and is produced in large quan¬ 
tities. This may be illustrated in the following manner: 

A red-hot iron rod has intensely high temperature, yet 

22 


VOLTAIC ELECTRICITY. 


23 


it does not contain nearly so mucli actual heat as the 
water of a single hot bath. The electricity of friction 
may be compared, therefore, to the heat of a red-hot 
iron rod ; that of chemical action to that of a large 
volume of warm water. 

26 . What is a voltaic or galvanic cell f 

An organization whereby chemical energy is trans¬ 
formed into electricity. Its simplest form consists of 
two dissimilar metallic plates, immersed in some liquid 
capable of acting chemically upon one more than upon 
the other. The surface less acted upon is called the 
negative plate, and that more acted upon the positive 
plate. Zinc is almost always used 
as the positive plate, and the differ¬ 
ence of potential, and consequently 
the electro motive force, is the great¬ 
est when there is no chemical ac¬ 
tion on the negative plate. The 
positive electricity is assumed to 
set out from the zinc, pass through 
the liquid to the negative plate, and 
thence by a connecting wire back again to the zinc. 
Such a cell is called a simple battery, and has one 
great disadvantage—namely, that when its circuit is 
closed, by connecting its poles by a wire, its action 
rapidly diminishes ; it becomes polarized. Many cells 
have been devised, chieffy with a view of diminishing 
or suppressing this fault of polarization, and thereby in¬ 
creasing the constancy of batteries. 

27 . What is meant by the term “polarization ” when applied to 
voltaic cells i 

We know that water is a chemical compound of two 
gases, oxygen and hydrogen. When the circuit of a 
simple zinc and copper battery is closed, chemical ac¬ 
tion commences and the water is decomposed, the oxy¬ 
gen attacking the zinc and eating it away, while the 
hydrogen deposits itself on and covers the surface of the 
copper plate, and, in fact, assumes nearly the same rela- 












24 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

tion to the zinc as if it were a zinc itself, the result being 
much the same as if two zinc plates were opposed to 
each other. A new electro-motive force is developed in 
opposition to the original electro-motive force of the 
battery; the working is impeded and the strength of 
current diminished. To this deleterious action is given 
the name of polarization . 

The injurious effects of polarization are increased by 
the power which hydrogen in this form has of reducing 
metals from their solutions ; for as soon as the sulpliate- 
of-zlnc solution formed by the action of the acidulated 
water on the zinc plate has diffused itself through the 
liquid so as to reach the copper, it is decomposed by 
the before-mentioned hydrogen, and metallic zinc is de¬ 
posited on the copper plate. This also tends to trans¬ 
form the battery into one wherein both plates are zinc. 

To render a battery constant (which means to furnish 
a steady and equal current during the time for which it 
works) polarization must be prevented. This object is 
attained in different ways ; in the Daniell battery, for 
example, by surrounding the negative plate with a 
strong solution of a salt of its own metal. This ex¬ 
pedient keeps the free hydrogen actively employed in 
reducing copper from the sulphate-of-copper solution 
and depositing it on the copper plate, and consequently 
restrains it from assuming a gaseous form and coating 
the copper plate ; and, further, as the metal reduced is 
the same as the plate itself, the battery gains instead 
of loses, because the surface of the plate, by the metal 
added, is kept new and bright. 

28 . What is a voltaic battery t 

When a series of voltaic cells are connected together 
as shown in Figure 7 the combination is called a voltaic 
battery , just as a combination of Leyden jars is desig¬ 
nated an electrical battery. The several elements of a 
battery may be connected together in several different 
ways, and this is regulated by the character of the work 
which the battery is required to do. 


VOLTAIC ELECTRICITY. 


25 


. A v °ltaic battery, to approach perfection, should be 
simple in construction, easily prepared and maintained, 
have a sufficiently high electro-motive force, be fairly 
constant, tolerably free from local action, economical 
in first cost, and consist of materials which are easily 
procured. 



Fig. 7. 

29 . What is meant by the term “ local action ” f 

It is a name given to chemical action which takes 
place in the battery, whether there is or is not any 
external metallic connection between the plates, or, in 
other words, whether the circuit is closed or open. It 
goes on at the surface of the zinc, and consumes that 
metal without aiding in the production of the working 
current. It is supposed to arise from the presence of 
impurities in the zinc, on account of which one por¬ 
tion of the metal is in electrical opposition to the other, 
thus producing local currents, causing evolution of hy¬ 
drogen at some points and consumption of the zinc 
at others. This evil is remedied to a great extent by 
amalgamating the zinc plate. The surface of the metal 
is thereby reduced to the same condition at all points, 
and differences of hardness, softness, and crystalline 
structure are eliminated. The amalgamation of battery 
zincs is effected by simply rubbing them with mercury, 
after they have been thoroughly cleansed by immersion 
in dilute sulphuric or muriatic acid. 






































































































26 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


30 . Why is a voltaic battery sometimes called a “pile” t 
Because the tirst arrangement constructed by Yolta 
for evolving current electricity consisted of a great 
number of round pieces of zinc, copper, and moist cloth, 

piled alternately one upon another, as 
in Figure 8. It was literally a pile of 
discs, and the name, from early associ¬ 
ations, is still used (chiefly, however, 
by French electricians), though it has 
now entirely lost its special signifi¬ 
cance. 

31 . Under what general heads may nearly 
all voltaic batteries be classified i 

Singlefluid batteries , of which that 
of Smee may be taken as a type. 

Two-fluid batteries , which may prop¬ 
erly be subdivided into three classes. 
Of the first class the well-known 
Daniell is the representative. The 
second subdivision comprises the nu¬ 
merous forms of gravity battery, from 
the Callaud to the Watson. In the 
Watson battery an inverted leaden fun- 
W nel is used as the negative plate, and 
also as a repository for the copper 
Fig. 8.-The Voltaic pile, sulphate. The third subdivision in¬ 
cludes the strong-acid batteries, such as Grove's and 
Bunsen's. 

The third great class is that wherein depolarizing 
mixtures are used. These preparations are made from 
different oxides and chlorides. The Leclanche battery 
is the best-known and most notable example. 



32 . What batteries are 7iow in most general use i 
In America the principal forms used are : the gravity, 
chiefly Callaud’s form (although every other type finds 
its advocates); the Grove, the Daniell, the chromic-acid, 
the Leclanche, and the Smee. 

In England the Daniell and Leclanche are used for 


















VOLTAIC ELECTRICITY. 


27 


telegraphs, and the Grove and Bunsen for other practical 
purposes. 

In France the Leclanche and Marie Davy are chiefly 
in use, while those in favor in Germany are Meidinger’s 
and Siemens & Halske’s, both of which are modifications 
of the Daniell. In India the Minotto is used almost 
universally. 

33 . Describe the principal batteries used in the United States, 
and state the puiposes to which they are respectively applied. 

The gravity battery is so named because the two so¬ 
lutions, sulphate of zinc and sulphate of copper, are 
separated from each other by the difference in their re¬ 
spective weights, the saturated solution of copper being 
heavier than the zinc solution, when the latter is in its 
proper condition. 

John Fuller, in 1853, was the first to suggest the 
gravity battery. Cromwell F. Varley patented several 
varieties of this battery, which have since been re- 
patented by several other inventors. 

In the Callaud form the gravity battery is, as shown 
in Figure 9, constructed as follows : On the bottom of 



a glass jar is laid a copper plate, having two vertical 
plates attached in the form of a cross. This projects 
about three or four inches above the bottom of the jar,. 












































28 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

To this copper is connected an insulated wire, which is 
extended up through the liquid and forms the connect¬ 
ing link, to be fastened to the zinc of the next cell. On 
the copper plate is placed a layer of sulphate of copper. 
The zinc plate is then hung on a brass frame near the 
top of the cell, and the jar is charged with water or 
with a weak solution of sulphate of zinc. 

The chemical action of this battery is the same as that 
of the Daniell: the zinc is oxidized by the oxygen of 
the water ; the oxide of zinc combines with the acid set 
free from the sulphate of copper and forms sulphate of 
zinc, which remains dissolved, while the oxide of cop¬ 
per previously combined with the acid is reduced, by 
the action of the hydrogen of the water, to metallic 
copper, and is deposited on the copper plate. This 
battery is much used in telegraphy, having to a great 
extent superseded the Grove. It has also come into use 
for local circuits, to operate sounders and registers, and 
in furnishing motive power for signalling purposes on 
short telephone lines. 

The Grove battery was until the last eight years 
almost universally employed as a main battery for the 
American telegraphs, but is now rapidly being pushed 

aside by the more economical Cal- 
laud. The Grove cell consists 
simply of a plate of zinc, as the 
positive plate, in dilute sulphuric 
acid, surrounding a porous cell 
in which is a plate of platinum im¬ 
mersed in concentrated nitric acid. 

The Daniell, which is the orig¬ 
inal sulphate-of-copper battery 
and the forerunner of every type 
of gravity battery, is to some 

extent employed in electro-de- 

Fig. lo.-Danieirs Battery. position, gilding, and silvering, 

and has been much used as a local battery in tele¬ 
graph offices. It is shown in Figure 10 and consists 




























VOLTAIC ELECTRICITY. 


2 £> 


of a jar containing a cylinder of zinc, G, and a porous 
cup, P, containing a plate of copper, X. Tlie porous 
cup is placed inside the zinc and filled with dilute sul¬ 
phuric acid, with salt water, or with pure water. This 
construction admits of considerable variety. If desired 
the zinc may be placed in the porous cup and the 
copper in the outside vessel. The solutions would then 



Fig. 11.—Chromic Acid Battery. 


also have to be changed so that the copper would always 
surround the copper. It is unnecessary to describe the 
action of the Daniell cell, as it is precisely the same as 
that of the Callaud, which has already been considered. 

The chromic-acid battery, often in this country called 
the carbon, and occasionally the electro poion battery, 
has been much used for telegraph lines, and is at the 
present day largely employed for printing telegraphs, 
also for open-circuit work, such as burglar-alarms and 






































































































































































































30 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

domestic bell ringing. A cylinder of zinc is placed' in a 
glass jar, a porous cup inside the zinc, and a plate of 
carbon in the porous cup. The porous cup is tilled 
with a solution of bichromate of potash, and the outer 
cell with dilute sulphuric acid. Its arrangement is 
shown in Figure 11. 

The Leclanclie battery, which in 1870 was scarcely 
known, is now extensively used throughout the country 

as an open-circuit battery. It is eco¬ 
nomical, requires little attendance, and 
since the introduction of the tele¬ 
phone its use has more than doubled. 
A zinc rod is the positive element, and 
a mixture of crushed peroxide of 
manganese and broken carbon sur¬ 
rounding a carbon plate in a porous 
cup is the negative element. The car¬ 
bon plate is provided with a leaden 
cap, to which is attached a binding- 
screw. The porous cup is then set in 
a glass jar, which is filled to about two- 
tliirds its height with a solution of sal- 
ammoniac. This battery is well suited for electric bells, 
for signalling on telephone lines, and for Blake micro- 
phonic transmitters. It will keep in good order for 
months with very little attention. 

A modified Leclanche cell, in which the porous cell is 
dispensed with, is at present a very popular form, and 
is much used in connection with transmitting tele¬ 
phones. It was patented in 1875 ; and the depolarizer, 
instead of being packed round the carbon plate in a 
porous cup, is formed into a mass composed of equal 
proportions of peroxide of manganese and granulated 
carbon, held together by the admixture of from live to 
ten per cent, of a resinous cement; the carbon plate is 
enclosed in this mass, and the conglomerate mass sub¬ 
jected to strong pressure in a hot mould. 

The zinc forms one pole and the compound forms the 



























































VOLTAIC ELECTRICITY. 


31 


■other. Both are fitted with binding-screws and im¬ 
mersed in a sal-ammoniac solution. 

This form is shown in Figure 13. 



Fig. 13. 


34. lYhctt is meant by the “po/es” of a battery % 

The wires, binding-screws, or terminals of each of the 
plates of a battery are called the poles. Their names 
are always opposite to those of the plates they lead 
from. Much confusion has existed in the minds of 
many persons with reference to these terms—the posi¬ 
tive and negative poles of a battery, and the positive 
and negative plates of a battery. This, however, may 
be dissipated by observing that the term plate, metal, or 
element is applied to that part of the plate which is in 
the liquid, and the term pole to that part of the plate 
which is out of the liquid and which is attached to the 
conducting wire. The term ‘‘positive” is intended to 
signify that from whence the current of electricity pro¬ 
ceeds, while the ‘ ‘ negative ’ ’ signifies that which the 


























































































































































































































































32 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

current enters. Now, tlie electrical action commences 
at the surface of the more oxidizable metal, which is 
usually zinc; therefore we call the zinc the positive 
plate. The positive electricity passes through the 
liquid, and is received and collected by the other plate, 
generally copper or carbon, which is hence called the 
negative plate. It passes from the end of that plate 
and out at the continuing wire, which by the same rule 
is called the positive pole ; it then passes through the 
wire to the toil of the plate from whence it originally 
started, which is consequently called the negative pole. 
It will, then, be understood that each plate of a battery 
has opposite terms applied to it. 

In a zinc and copper battery the zinc is the positive 
plate, but the wire leading from it is the negative pole, 
while the copper is the negative plate, but the wire pro¬ 
ceeding from it the positive pole. 

35. What is the signification of the terms “ electrode “ elec¬ 
trolysis and “ electrolytewhich are frequently found in icorks 
on electricity f 

They are terms proposed by the late Professor Fara¬ 
day, and have been used by electricians in various ways. 
The poles, or plates, leading a current into and out of a 
battery were called by him electrodes —that is, ways or 
paths of electricity, from the Greek words electron and 
odos. An electrolyte is a compound decomposable by 
the electric force, and the term electrolysis means the 
act of such decomposition. 

36. Give some simple directions for the care of batteries. 

The Daniell, gravity, Grove, and Leclanche batteries, 
being types of all the principal batteries in use, will 
alone be noticed here. 

The Daniell Battery. —Use the best quality of copper 
sulphate procurable. Never use powdered sulphate, 
as it soon cakes and then dissolves too slowly to be 
of much use. Never use porous cups after they are 
cracked or any way damaged, or let the zinc touch the 
porous cup. If the zinc is used inside the porous cup,. 


VOLTAIC ELECTRICITY. 


33 


let it be suspended, so that it will not touch the bottom 
of the cup. 

The zinc solution is at its best when it is half satu¬ 
rated. When it is stronger than that point of satura¬ 
tion, a portion should be drawn off and the cell filled 
up with water. At least once in two months a Dan- 
iell battery should be thoroughly cleaned, the plates 
scraped, and any copper found attached to the porous 
cup scraped off. The copper solution, if clean, may all 
be restored, but half the zinc solution will usually be 
sufficient. 

The following hints may be given on the maintenance 
of the gravity battery : 

After setting up, if the battery is weak connect the 
poles by a wire for a day or two ; this will tend to sepa- 
rate the solutions and to concentrate the zinc sulphate 
solution. Keep the level of the water at- least a quarter 
of an inch above the zinc. Avoid shaking the solutions. 
Keep the line between the copper and zinc solutions as 
sharp as possible. 

If the blue is too low draw off a little of the upper 
solution with a syringe, and replace it with pure water ; 
then leave the battery circuit open when not being used. 

If the blue gets too high put the battery on short cir¬ 
cuit when not in use. 

If a froth generates on the surface remove it with a 
piece of wood or a brush. 

If the zincs become very dirty take them out, scrape 
and wash them. 

Jars should never touch each other. Shelves should 
not be allowed to become dirty. Generally speaking, if 
the blue rises too high the resistance in the circuit is too 
great for the battery. 

Be sure that the covering of the insulated wire leading 
up from the copper plate is perfect ; and in setting up a 
battery never use old material, unless it is in every re¬ 
spect good. 

The Grove Battery .—The zincs of this and all other 


34 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


acid batteries should be kept well amalgamated in order 
to prevent local action. Grove batteries should be taken 
apart every night; one-tenth of fresh nitric acid should 
be added every morning, and the dilute sulphuric acid 
renewed twice a week. 

Use great care in handling the acids, as they are very 
corrosive. Place the zincs every night in water weakly 
acidulated with sulphuric acid. 

The Leclanche Battery .—Never let the outside solu¬ 
tion rise above the shoulder of the jar. When setting 
up the battery pour a little water in the porous cup. 
The sal-ammoniac solution should be saturated, but too 
much sal-ammoniac ought not to be put into the jar at 
once, as it is apt to cake instead of dissolving. When 
the solution becomes too weak, crystals of oxychloride 
of zinc form on the zinc and weaken the action of the 
battery. 

Watch the connecting wires carefully, as they are 
liable to be eaten through by the free ammonia gene¬ 
rated in the battery. If the battery is weak, and no 
cause is apparent, test each cell separately, and, when 
the defective cell is found and examined, probably a 
salt of lead will be found between the lead cap and the 
carbon plate, partially insulating it. Renew the water 
in the outside vessel when necessary, at the same time 
adding a little sal-ammoniac. 

If by accident the Leclanche cell be left on closed cir¬ 
cuit and run down, its strength may be to a certain 
extent renewed by soaking the porous cups in water 
or dilute muriatic acid and giving the battery a con¬ 
siderable rest. 

Rolled zinc should be used in preference to cast, as it 
is purer and more economical in the end. 

The following hints are applicable to all batteries : 

Insulate each cell perfectly, and keep the shelves on 
which they stand clean and dry. Keep all points of 
contact and all connections clean and bright. No leak¬ 
age or creeping of liquids from the cells should be al- 


VOLTAIC ELECTRICITY. 


85 


lowed, and as soon as any sucli tiling shows itself it 
should be wiped away with a damp cloth. To prevent 
such action the edges of the outside vessel should be 
dipped in melted paraffine. The temperature of a battery 
room should not be too warm, or the liquids will evapo¬ 
rate ; nor too cool, or they will lose power. Solutions 
should always be renewed before they are exhausted, 
and the batteries periodically examined, so that any 
defect will be located and removed before causing any 
radical trouble. Every connection must be made tight 
and kept free from oxide. 

37. How is the presence of iron in sulphate of copper detected i 

The suspected crystals must be dissolved in water, 
and liquid ammonia added to the solution. This will at 
first q>recipitate both copper and iron, and the solution 
will appear very cloudy. More ammonia is then to be 
added, when the copper will be redissolved, forming a 
bright blue solution, and the iron, if present, will fall to 
the bottom in the form of a brown powder. 


CHAPTER III. 


THERMO-ELECTRICITY. 

38. What is thermo-electricity i 

Thermo-electricity is the name given to that branch of 
the science of electricity which relates to the production 
of electric currents by the agency of heat. 

The term literally means heat-derived electricity. 

Professor Seebeck, of Berlin, in 1823 discovered that 
if two bars of any two metals, especially bismuth and 
antimony, be soldered together at one end, and have 
their other ends connected with one another by a wire, 
so as to form a complete circuit, on the application of 
heat to the point where the metals are soldered a por¬ 
tion of the applied heat is absorbed and disappears, and 
an electric current is developed in its stead. 



Fig. 14.—Electricity produced by Heat. 


All metals, and many other conductors of electricity, 
are capable of producing thermo-electric currents, and 
they are all classed either as thermo-electro-positive or 
tliermo-electro-negative bodies. The former class com¬ 
prises those conductors in which the current proceeds 
from the colder to the warmer portion ; and the latter 

36 













THERMO-ELECTRICITY. 


37 



Fig. 15.—Thermo-electric 
Battery, with Galvanometer. 


includes those in which the current proceeds in the 
opposite direction. 

Bismuth may be regarded as the representative of the 
former class, and antimony as that of the latter. In ex¬ 
periments in this science, therefore, these metals are 
most frequently used. For example : We take a bar of 
bismuth, and solder or braze one 
end of it to one end of a bar of an¬ 
timony, then attach a galvanometer 
by wires to the free ends of the two 
bars, so that the circuit is completed 
from the bismuth to the antimony 
by soldering ; then from the other 
end of the antimony to one terminal 
of the galvanometer, and from the 
other terminal of the galvanometer to 
the free end of the bismuth. If we 
then heat the junction of the two 
bars we shall see the needle deflect, 
the current proceeding from the bismuth through the 
heated point to the antimony, thence through the gal¬ 
vanometer and back to the bismuth. Some metals when 
thus united are found to produce a current in one direc¬ 
tion when the junction is moderately heated, but when the 
heat is increased the direction of the current is reversed. 

39. What is a thermo-electric battery f 

When only one bar of 
each of the metals employ¬ 
ed is used the arrangement 
is called a thermo-electric 
pair. A number of these 
thermo-electric pairs may 
be joined in series, just as a 
number of voltaic cells are 
joined together for the for¬ 
mation of a voltaic battery. 

When the pairs are so joined the entire series is 
called a thermo-electric battery , and its electro-motive 




Figs. 16 and 17.-Nobili’s Thermo-electric 
Battery. 









































38 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


force is equal to the sum of the electro-motive forces 
of all the pairs added together. To make such a 
battery, suppose we have six bars of bismuth and the 
same number of antimony, each bar being three inches 
long, three-quarters of an inch wide, and one-fourtli of 
an inch thick. Arrange them alternately, so that if the 
first bar is bismuth the last will be antimony. The bars 

4 / 

must then be soldered together at each end, the sec¬ 
ond, antimony, being, for instance, at one end soldered to 
the first bar and at the other end soldered to the third ; 
the third, in its turn, having its other end soldered to 
the fourth, and so on. The two terminal bars will, of 
course, have one end unattached. These free ends rep¬ 
resent the poles of the battery. To set the battery in; 

operation all the junc¬ 
tions on one side must 
be heated, while all 
those on the other side 
must be kept cold. 
While the arrangement 
described represents the 
principle of the thermo- 
battery there are many 
varieties, modifications, 
and improvements. One 
of the first thermo-bat¬ 
teries was invented by 

Fig. 18.—The Thermo-electric Multiplier for Mea- jVXelloni ill 1834. He 

curing neat. made what he called a 

thermo-multiplier. It consisted of about fifty little bars 
of antimony and bismuth enclosed in a brass cylinder, 
the whole arrangement being but two and a half inches 
long and about half an inch in diameter. The termi¬ 
nal bars were connected by wires to a delicate gal¬ 
vanometer. This contrivance was so sensitive to slight 
changes in temperature that when the hand was brought 
near to one end of the instrument the current generated 
was sufficient to move the needle several degrees. Two 




























THERMO-ELECTRICITY. 


39 


of the most efficient thermo-electric batteries are those 
of Noe, of Vienna, and Clamond, of Paris; the former 
being more speedily excited and giving a powerful 
current, and the latter being very strongly constructed. 
To sum up : A thermo-electric battery may be briefly 
defined as a device which transforms heat into elec¬ 
tricity. 

40. Has the thermo-electric battery ever been employed for 
practical purposes f 

\ es, it has been applied to several purposes. Mel- 
loni, at a very early date, used the thermo-pile, previ¬ 
ously described as having been constructed by him, to 
measure small differences in temperature. Clamond’s 
battery has been quite extensively experimented with in 
England for working telegraph circuits. It was expect¬ 
ed that the thermo-electric x>ile, in Clamond’s improved 
form, would, on account of its low resistance, be useful 
as a universal battery—that is, one from which many 
circuits are worked ; and at one time five thermo-batter¬ 
ies were used to work no less than ninety separate 
circuits from the London post-office. Each of these cir¬ 
cuits was less than one hundred miles in length. All 
the thermo-batteries, however, ultimately failed by the 
burning out of the insulating material between the 
several layers of bars. This is probably not a fault 
which will prevent the thermo-pile from being eventually 
used. 

But the mo3t important application of the thermo¬ 
electric batterv has hitherto been to furnish a current 
for the electro-deposition of metals, or, to use more fa¬ 
miliar terms, for electro-plating. It was first so used in 
1843 by Moses Poole, and patented, but did not then 
come into general use. Thermo-electricity has, however, 
been more or less employed since that time for plating, 
and, since the invention of Clamond, has done efficient 
work. Clamond’s thermo-electric battery is now in use 
in various plating establishments in Birmingham, Lon¬ 
don, and Sheffield, and it is said that a machine of one 


40 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

hundred bars, with a consumption of eight to nine feet 
of gas, deposits an ounce of silver per hour. 

These batteries have experienced such important im¬ 
provements of late years that it is believed they will 
soon be utilized with great advantage. 


CHAPTER IV. 


EARTH-CURRENTS AND EARTH-BATTERIES. 

41. What are earth-currents i 

They are currents which are always flowing through 
telegraphic lines, and which depend for their existence 
on a difference of potential between the two points of 
the earth at which the line is terminated. They are, 
therefore, currents flowing from one part of the earth to 
another, which, being of course subject to the ordinary 
laws of electricity, and finding another path open to 
them at the ground-plate where they enter, divide there, 
part of the current taking the wire route to the distant 
point, the other part taking the route through the 
earth. 

They vary in strength at different periods in the day 
and year, and sometimes are so strong as to render the 
working of a line difficult. They are then called electric 
storms. 

Sometimes they flow in one direction, sometimes in 
the other, and in any case are very unwelcome visitors 
in telegraph lines. 

They are particularly frequent on long cables, and en¬ 
danger the safety of the cable. They also render test¬ 
ing with the galvanometer very uncertain and incorrect. 

42. How may the effects of earth-currents on telegraph lines 
he obviated % 

On ordinary telegraph lines this may be done in two 
ways : The first mode may be adopted when two wires 
run parallel to each other; it consists in abandoning 
the use of the ground-wires at the terminal offices, and 
looping the wires, so as to form a metallic circuit. In 
practice, if the wires are looped together at but one end 
the result is satisfactory. 


41 


42 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


The second method may be used where there are not 
two wires parallel to each other, and is effected by re¬ 
moving the ground-wire at one end of the line and 
lengthening the circuit by connecting another line run¬ 
ning in another direction to it, so that if a straight line 
were drawn connecting the two end offices it would be 
out of the direction of the earth-current prevailing at 
the time. 

In the case of submarine cables of considerable length 
the same result is effected by the use of condensers, 
which are interposed between the ends of the cable and 
the ground. 

43. Are there any other currents which appear on telegraph 
lines without apparent cause i 

Yes. If the earth-plates of a circuit are of different 
metals a permanent current will be set up, varying in 
strength according to the metals used. For example, 
if a copper plate be buried in the earth at one end of 
the line, and a zinc plate at the other, the current will be 
comparatively powerful. If one earth-plate be of lead 
and the other of iron, the current will not be as strong 
as that developed by the copper and zinc, but it will still 
be quite perceptible. 

This may readily occur, and to the inexperienced 
electrician sometimes proves very puzzling. If, for in¬ 
stance, the wire be grounded on an iron gas-pipe at one 
end of the line and on a lead water-pipe at the other, 
and a current appears, as under the circumstances it 
surely will, it needs some experience to determine its 
origin. When suspected one ground or the other must 
be changed until no current passes. 

This current hns been utilized under the name of the 
earth-battery current. It was used by Gauss in Ger¬ 
many at an early date, was subsequently employed by 
Bain to work electric clocks, and in 1846 was used by 
Steinheil on a Bavarian telegraph line twenty miles long. 
For telegraphs, however, it has not attained any re¬ 
markable degree of success. 


CHAPTER Y. 


MAGNETISM—ELECTRO-MAGNETISM AND ELECTRO¬ 
MAGNETS. 

44. What is magnetism % 

It is the name given to the science which treats of the 
peculiar properties of attraction, repulsion, polarity, and 
the development of magnetism in other magnetic bodies 
by induction, which are possessed, under certain condi¬ 
tions, by iron and some of its compounds, and in inferior 
degree by nickel. The metals cobalt, chromium, and 
manganese also possess magnetic properties to a limited 
extent. 

The term is also employed to denote the cause of mag¬ 
netic phenomena. The name is generally supposed to- 
be derived from Magnesia, a place in Asia Minor, where 
the natural magnet was originally found by the Greeks. 

The existence of magnetism is noticed in very ancient 
Chinese, Greek, and Roman manuscripts. 

45. What is a magnet t 

A body which exhibits magnetic properties is called a 
magnet. The name is usually confined to the ferrous 
substances mentioned above (44); but all conductors of 
electricity are capable of showing similar effects while 
conveying a current. 

46. What is a natural magnet f 

The natural magnet, often also called the loadstone, is 
an ore of iron, called by chemists ferrosoferric oxide. 

It is known by the symbol F 3 O 4 , and is by minera¬ 
logists termed magnetite. It is generally met with in 
small pieces, but sometimes occurs of quite a large size. 

It is composed of about seventy-three parts iron and 

43 


44 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

twenty-seven oxygen. First found in Magnesia, in Asia, 
it has since been procured from many other places, and 
at the present time the most powerful natural magnets 
are found in Siberia and in the Harz Mountains of Ger¬ 
many. 

The natural magnet has been known in almost every 
country from the earliest ages, and in nearly every lan¬ 
guage the name given to it is based on its supposed 
partiality for iron. The English name loadstone is de¬ 
rived from the Saxon word Icedan (to lead), a name sug¬ 
gested by observation of its directive power. 

The attractive force of the natural magnet is not great 
in proportion to that exhibited by artificial magnets, as 
it is very seldom that a piece is met with that will sus¬ 
tain its own weight. 

47. What is an artificial magnet f 

It is a body possessing all the properties of the natu¬ 
ral magnet, these properties having been imparted to it 
by artificial means. If a bar of hard steel is repeatedly 
rubbed from end to end by a magnet, the steel receives 
all the magnetic properties. Or if such a bar is placed 
within a helix of insulated wire, and a current of elec¬ 
tricity passed through the helix, the bar becomes mag¬ 
netic. A piece of steel thus acted upon is an artifi¬ 
cial magnet. 

The property which magnets have of imparting mag¬ 
netism to steel is extremely valuable, as steel can be 
easily shaped into any required form, and utilized in 
many ways and for many purposes that a natural mag¬ 
net could not be applied to. 

48. TTViaf are the characteristic properties of magnets i 

First, Attraction. This property resides principally 

in two opposite points. These points are called poles. 
When either pole of a magnet is brought near to a piece 
of iron a mutual attraction takes place between them. 
The reason is that the iron also becomes magnetized by 
its proximity to the magnet, the part which is nearest 
to either pole of the magnet acquiring an opposite polar- 


ELECTRO-MAGNETISM AND ELECTRO-MAGNETS. 45 


ity to it, causing tlie iron to attract the magnet with a 
force equal to that with which the magnet attracts the 
iron. Thus it will be seen that the 
attraction which a magnet appar¬ 
ently lias for iron is really an attrac¬ 
tion for the opposite pole of another 
magnet, as graphically shown in 
Figure 19. 

Second, Repulsion. This is seen 
in the action of two magnets upon 
each other. If two magnets are 
suspended so that they can move 
freely in an horizontal plane, and 
their similar poles are placed close 
together, they will be observed to 
repel each other and turn round 
until their opposite poles are in 
juxtaposition. Or if, as in Figure 
20, one of the magnets, s n , is sus¬ 
pended, and the second, N S, is 
brought close to it, the north pole 

sented to the north pole 
of the other, a quick re¬ 
pulsion takes place ; the 
same occurring also if two 
south poles are brought 
together. 

Thus the two magnetisms 
in this have a resemblance 
to the two electricities: 
like poles repel; opposite 
poles attract. 

Third, The power of de¬ 
veloping magnetism in 
iron or steel by induction. 

rig. 20 .— Mutual Action of Magnetic roles. Whenever magnetic prop- 

erties are developed in bodies not previously possessed 
of them, the process is called magnetic induction ; and 































































46 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

for such, development it is not necessary that the body 
shall be brought into actual contact with the magnet. 

By bringing a magnet near to iron or steel the latter 
bodies are rendered magnetic by induction; are then 
capable of attracting iron, and themselves possess the 
power of communicating the properties to other pieces 
of iron. This is especially the case with soft iron, and 
it is only while the iron remains in the vicinity of the 
magnet that it retains these qualities. 

As soon as the magnet is withdrawn, the iron loses its 
induced powers. With steel and hardened iron the 
case is different. When iron is hardened magnetism is 
induced more slowly, and is more slowly parted with ; 
and when magnetism is induced in hardened steel it re¬ 
quires, as it were, to be rubbed in. 

When once thoroughly magnetized the piece of steel 
is a permanent magnet. 

Fourth, Polarity . If a magnet is suspended so as to 
move freely in a horizontal direction it will always come 
to rest with the same pole pointing to the north, as in 
Figure 21. 

This property is called polarity, or directive force, and 
is familiarly illustrated by the ordinary compass. If the 

magnet is suspended so as to 
move freely in a vertical plane, 
it will be found to have the 
power of inclining itself to the 
horizon at various angles, ac¬ 
cording to the locality. This 
power is called the dip of the 
magnet. 

North of the equator the ex¬ 
tremity that points to the north 

Fig. 21. Directive Action of the Earth, djpg ; south of tile equator the 

other end dips. The dip varies with the latitude. Near 
the equator the needle lies nearly level, while near 
the north and south poles it verges on an upright 
position. 












ELECTRO MAGNETISM AND ELECTRO-MAGNETS. 47 


In the latitude of New York the angle of dip is about 
seventy degrees. 

49. What are the poles of a magnet i 

The extremities of a magnet, where its magnetic 
powers most clearly manifest themselves. In a bar 
magnet the poles are found very nearly at the ends. 
The earth is itself a magnet, and has north and south 
magnetic poles. The pole which in any magnet points 
to the north is called the north pole, and the other is 
called the south pole. Any two north poles repel each 
other, as do also any two south poles ; but any north 
pole attracts any south pole, and nice versa. 

. The poles of the magnet are shown in Figure 22, in 
which iron filings are seen to accumulate at both ends 
of the bar, while 
the middle does 
not attract them 
at all. 

Hence the di¬ 
rective power of Fig. 22.—The Magnet. 

the magnet. The north pole of the earth attracts the 
opposing pole of the magnet, which, strictly speaking, 
should therefore be called the south pole; but it has 
long been customary in English-speaking countries to 
call the pole pointing to the north the north pole, hence 
it would now tend to create confusion if the practice 
were changed. 

If a magnet be broken in two each piece becomes a 
complete magnet, with north and south poles. 

It has been found desirable for practical purposes to 
distinguish the two poles by marking one of them— 
usually the extremity which points northward—with a 
small file-cut. Another method is to color the north 
pole blue and the south pole red. 

50. What is a permanent magnet ? 

As previously noticed, steel (which is a compound of 
iron with carbon), while it acquires magnetism with 
difficulty, retains its magnetism more or less perma- 




















































48 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

nently, after tlie withdrawal of the inducing magnet* 
This difficulty in the reception of magnetism, and the 
permanency with which, when once acquired by steel, it 
is retained, is called coercive force. 

On account of the latter property a magnet formed of 
hard steel is called a permanent magnet. 

Permanent magnets may be of any required form, but 
for general purposes only two styles are made—namely, 
bar and horseshoe magnets. 

51. Describe the bar , horseshoe , and compound magnets. 

A bar magnet is an artificial permanent magnet in the 
form of a straight bar. The magnetic needles used in 
telegraph instruments and compasses are delicate bar 
magnets. 

A magnet which is bent in such a manner as to bring 
its two ends, or poles, near each other, so that they can 
be connected by a short, straight piece of iron, is called 
a horseshoe magnet. Magnets for general use are most 
frequently made in this form, because it is then easier to 
bring both poles into play upon the same object. 

The short piece of iron spoken of as being used to 
connect the poles of a horseshoe magnet should be of 
soft iron. It is called an armature , or keeper , and when 
the magnet is not being used, the armature, to prevent 
the loss of power, should be constantly kept across its 
poles. 

A compound magnet consists of two or more bar or 
horseshoe permanent magnets, placed side by side and 
fastened together, with their similar poles in contact. 

They are arranged in this way for the purpose of in¬ 
creasing the magnetic power. 

Although a compound magnet is stronger than any of 
its component magnets, it is very much weaker than the 
sum of the strengths of all the magnets, were they used 
separately. This is because the similar poles of all of 
them, being laid close to one another, have a tendency 
to react on each other, and, to a certain extent, induce 
an opposite polarity in the contiguous magnets. 


ELECTRO-MAGNETISM AND ELECTRO-MAGNETS. 49 

52. Describe the process of magnetizing steel for the forma¬ 
tion of permanent magnets. 

There are several different methods of magnetizing 
steel bars, needles, and horseshoes, among which may 
be noted the following as the most important and the 
most generally used. Small needles can be magnetized 
by merely placing them across the poles of a permanent 
magnet for a short time. One of the simplest ways to 
magnetize a steel bar is to place the middle of the bar on 
one of the poles of a strong bar or horseshoe magnet, and 
draw one end of it over the pole a number of times, never 
failing to draw it from the middle to the end ; then turn 
the bar end for end and repeat the process, drawing the 
other end over the other pole of the permanent magnet. 
The end that has been drawn over the north pole of the 
permanent magnet will possess south polarity, and the 
other will possess north polarity. 

A horseshoe can be magnetized by drawing it over the 
two poles of a permanent or electro magnet in such a 
way that both halves of the horseshoe pass at the same 
time over the poles to which they are applied. If it is. 
thick it should be turned over, and the process repeated 
on the opposite side. 

But of all the modes practised the most efficient is the 
use of the electric current. A helix is prepared, con¬ 
sisting of a number of layers of insulated wire. It has a 
small central opening, and when a steel bar is placed in¬ 
side the opening, and a strong current passed through 
the helix, the bar is strongly magnetized. 

53. What is the meaning of the term “ magnetic field ” f 

The presence of a magnet always modifies in some way 

its immediate neighborhood, so. that pieces of iron and 
steel brought into the proximity of the magnet acquire 
magnetic properties by induc tion ; and any other magnet 
placed there shows at once that it experiences a pecu¬ 
liar force. 

This locality immediately surrounding the magnet is 
called the magnetic field , and the term literally means 


SO ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

the extent of space surrounding the poles of a magnet 
in which the magnetic forces may be recognized. 

54. What is diamagnetism i 

In 1845 Faraday demonstrated the magnetic condi¬ 
tion of all matter, and showed that all bodies divided 
themselves into great classes—the one attracted, the 
other repelled—by the poles of a magnet. As the force 
producing the former result is called magnetism, he 
gave to the force causing the repulsion the name dia¬ 
magnetism, or cross-magnetism. And any substance 
which, when delicately suspended between the poles of 
a magnet, instead of settling across from pole to pole, 
arranges itself transversely to that position, so that it 
points in the same direction as the magnet and is re¬ 
pelled by both poles alike, is called a diamagnetic body. 
The bodies which most strongly exhibit this force are 
bismuth, antimony, and zinc. But the force of diamag¬ 
netism is, at its best, much feebler than that of ordinary 
magnetism, as bismuth, which is of all substances the 
most strongly repelled, is still repulsed with a force so 
much less than that exerted in the attraction of iron as 
to bear no comparison to it. 

55. What is the nature of the relation between electricity and 
magnetism , and by idiom was this relation discovered f 

The discovery of the relationship between electricity 

and magnetism was an ob¬ 
ject eagerly desired and 
sought for by the electri¬ 
cians and scientists of the 
last century, but for such 
a protracted period without 
result that it was doubted, 
and by some even denied, 
that any such relationship 
existed. But in the year 
1820 Hans Christian Oersted, professor of natural phil¬ 
osophy at Copenhagen, announced his discovery that if a 
wire conveying an electric current be placed horizontally 


















ELECTRO-MAGNETISM AND ELECTRO-MAGNETS. 51 

above a magnetic needle, and parallel to it, tlie needle is 
deflected, as represented in Figure 23, and tends to place 
itself at right angles with the conducting wire, the end 
of the magnet nearest the positive pole of the battery de¬ 
flecting eastward. 

If the conducting wire be similarly placed under the 
needle all the effects are the same, except that they are 
in an opposite direction. 

This relationship, described in plain language, consists 
literally in the fact that a wire electrified by a constant 
source or stream of electricity becomes practically a 
magnet (or, to speak more correctly, a straight current 
produces in a wire a magnetic field, in which the lines 
of force are circles concentric with the wire), and dis¬ 
turbs the magnetic field of the earth’s magnetism, con¬ 
sequently tending to deflect a magnetic needle, pivot¬ 
ed within the sphere of its influence, from its position 
pointing north and south. 

The fact of the deflection of the magnetic needle, 
when placed near a wire conveying a current, had been 
previously discovered and announced as early as 1802 
by an Italian philosopher, Gian Domenico Romagnesi, 
of Trent ; but owing to the limited publicity he gave to 
his discovery, and to the unprepared condition of the 
scientific world at that time, it attracted no notice un¬ 
til rediscovered by Oersted. 

From the foregoing facts, when announced by Oersted, 
Ampere, of France, made the deduction that “magnet¬ 
ism is the circulation of currents of electricity at right 
angles to the axis joining the poles of the magnet.” 
Arago (also a French scientist) shortly after show T ed 
that every conductor of electricity, while conveying a 
current, becomes possessed of magnetic powers, and in 
the same year discovered that current electricity would 
magnetize small pieces of iron and steel; and he accom¬ 
plished this by placing them in a glass tube and wind¬ 
ing a wire, which connected the two poles of the battery, 
round the tube. Sir Humphry Davy, of England, like- 


52 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

wise in 1820 found that sewing-needles could be mag¬ 
netized by merely rubbing them across a wire convey¬ 
ing electricity. From this time electrical discovery has 
been rapid and progressive. 

The two forces are so intimately connected that by 
many scientists they are considered to be only different 
manifestations of the same agency, the motion of a 
magnet always producing electricity, and the transfer of 
electricity as uniformly producing magnetism. 

56. What is electro-magnetism i 

It is that department of electrical science which re¬ 
lates to the development of magnetism and the deflection 
of magnetic needles by means of electrical currents. 

57. What is an electro-magnet i 

A helix of wire conveying a current of electricity lias 
magnetic properties. If such a spiral be made of insu¬ 
lated wire and wound on a bar of soft iron the iron be¬ 
comes magnetized and its force is added to that of the 
coil. The combination of the coil and the iron together 
is called an electro-magnet. Electro-magnets .may be 
made of any form, but the most common forms are the 
bar, in which the poles are as far apart as possible, 
and the horseshoe, in which the poles are as close to¬ 
gether as possible. 

For practical purposes they are made by winding 
covered copper wire on two bobbins or spools, a a', pass¬ 
ing soft iron cores, c c', through them, 
fixing the two soft-iron cores on a 
connecting-piece or yoke, b, also of 
soft iron, and connecting the two 
spirals together in such a manner 
that if the cores were straightened 
out into one bar the wire would be 
coiled in the same direction from 
one end to the other. 

The ends of the cores are called the poles of the elec¬ 
tro-magnet. 

An electro-magnet has, as long as the current flows 




















ELECTRO-MAGNETISM AND ELECTRO MAGNETS. 53 


in the coils, all the properties of a permanent magnet, 
and can be made to possess much greater power than 
a permanent magnet of the same size. The magnetic 
force developed in any electro-magnet is dependent on 
the strength of current, the number of turns the wire 
takes round the core, and the size of the iron core itself. 

The first electro-magnet was made in 1825 by Stur¬ 
geon, but a practical and useful one was not produced 
until 1830, when Professor Henry constructed the first 
magnetic spool or bobbin ever produced, by winding in¬ 
sulated wire round a soft-iron core, and by so doing ex¬ 
alted the power of the electro-magnet in an astonishing 
degree. 

58. What is residual magnetism i 

We have seen that when a piece of soft iron is brought 
near to a magnet it becomes magnetized by induction, 
-and that when removed from the influence of the mag¬ 
net it loses all trace of its induced magnetism. This is 
also the case with electro-magnets. When a current is 
conveyed through the coil of the electro-magnet the 
soft-iron core is strongly magnetized; and when the 
circuit is broken, or from any cause the current ceases 
to flow, demagnetization instantly takes place. It is 
this property that makes the electro-magnet so valuable 
and so universally useful. It must be observed, how¬ 
ever, that this complete demagnetization is dependent 
on the quality and softness of the iron. If it is not 
very soft and pure, or, in the case of an electro-magnet, 
if the armature is allowed to touch the poles, a certain 
amount of magnetism remains in the iron, and is called 
residual magnetism. Hence the iron used should be of 
the softest and purest kind, old Swedish iron being pre¬ 
ferable. 

59. In making calculations on the strength of electro-magnets 
is the resistance of the battery to be taken into consideration t 

In short circuits, where the resistance is proportion¬ 
ately large to the resistance of the rest of the circuit, it 
should be. For example, in a local circuit of a Morse 


54 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

sounder there is practically no resistance outside of the 
sounder-coil, except the battery. It is obvious, then, 
that it must be considered and the coil made equal to 
it. But when the battery of a very long external cir¬ 
cuit is in question it is not necessary to include the re¬ 
sistance of the battery with that of the circuit, because, 
though large, it, is yet, in proportion to the rest of the 
circuit, very small, and to sinqiLify the calculation it is 
usually ignored. 

60. Has the length of the iron core any effect on the icorking 
of an electro-magnet i 

Yes. Electro-magnets with short cores charge and 
discharge more rapidly than those with long ones. Ad¬ 
vantage of this fact has been taken in telegraphy, and 
all the later forms of relay have short cores. A magnet 
also works quicker when charged by a battery of many 
veils than when few are used. When strength rather, 
than speed of action is required it is well to employ 
magnets with long cores, because the convolutions of 
wire can then be increased in number without decreas¬ 
ing their distance from the core, by adding a great num¬ 
ber of layers of wire. 

61. What proportion should the resistance of an electro-mag¬ 
net hear to the resistance of the other component parts of the 
circuit i 

It is one of the laws of electro magnetism that with 
any given battery the greatest magnetic force is obtain¬ 
ed when the resistance of the coils of the electro-mag¬ 
net or magnets is equal to the resistance of the other 
portions of the circuit—that is, of the batteries and con¬ 
ducting wires. This law holds good practically on short 
and local circuits ; but on long telegraphic circuits it is 
only applicable when they are perfectly insulated. It 
is, therefore, usual in telegraphic practice to make the 
total resistance of the electro-magnets considerably less 
than that of the line, when in good order, so that in bad 
weather the best results may be obtained. 

To illustrate: It is required to ring a bell over a copper 


ELECTRO-MAGNETISM AND ELECTRO-MAGNETS. 55 


wire one hundred feet long, with two cells of Leclanche 
battery. What should be the resistance of the bell-mag¬ 
net to obtain the greatest magnetic power? The Le¬ 
clanche cell has an internal resistance of about one ohm; 
therefore two cells would have a resistance of two ohms, 
and in this case the conductor, on account of its short¬ 
ness, may be ignored. The resistance of the bell-magnet 
need be only two ohms to obtain the best result. The 
consideration of wire conies in here. Although we have 
decided that the resistance of the coils should be two 
ohms, it is still possible to err in the size of wire em¬ 
ployed ; therefore after ascertaining, by the relative re¬ 
sistances of the circuit and the rule already given, what 
the resistance of the electro-magnet should be, we must 
take care not to use wire that is too line, or we shall 
reach the required resistance before the core is suffi¬ 
ciently covered to give much magnetic effect, as with 
very line wire it takes very few convolutions to give a 
resistance of two ohms. 

It is essential not to use wire that is too coarse, as in 
that case we have to wind so many layers that, except 
in the first one or two layers, the convolutions are so far 
away from the core as to lose their influence on it. Wire 
should always be chosen, therefore, for winding electro¬ 
magnets that will reach the required resistance before 
the last convolution attains a distance of half an inch 
from the core. Between half an inch and three-eightlis 
from the core is the best distance for the last layer of 
wire. 

We will now suppose a line half a mile long, built of 
No. 9 iron wire, with two bell-magnets in circuit, and 
a battery of ten cells. The battery resistance is ten 
ohms, the line resistance about eight ohms ; total resist¬ 
ance of line and battery is, then, eighteen ohms. The 
sum of the electro-magnets should then, likewise, be 
eighteen ohms, or nine ohms each, to obtain the great¬ 
est magnetizing power from the given battery of ten 

cells. 


56 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

. 62. In constructing an electro-magnet for a very short cir¬ 
cuit what kind of wire should be used , and why ? 

We have seen that the resistance of the electro-mag¬ 
net coil should be equal to that of the other portions 
of the circuit. It is, therefore, apparent that to accom¬ 
plish this in a very short circuit it is necessary to em¬ 
ploy a comparatively short, coarse wire—short, because 
even a very small addition would increase the resistance 
of the circuit out of all proportion ; thick, because the 
current is not greatly enfeebled by its use, while the 
number of convolutions it allows of are sufficient to 
effect a strong magnetization. In short, we use a com¬ 
paratively thick wire because it is necessary to get the 
greatest magnetic effect without the weakening of the 
current consequent on the use of a thin wire, which 
necessarily is of high resistance. 

63. How should an electro-magnet be made for a very long 
circuitor a circuit of very high resistance , and why f 

Fora long circuit, such as that of a telegraph line, ora 
circuit which has a high resistance outside of the coil— 
for instance, in the battery—the magnet must be wound 
with a very fine, small wire of great length, which will 
allow of a great number of convolutions being wound 
over the core without exceeding the distance at which 
they cease to increase its magnetism. The reason of this • 
is that in a very long circuit, like a telegraph line, or 
in a circuit of very high resistance, the current is neces¬ 
sarily very weak and feeble, even though the battery be 
composed of a large number of cells. The coil is, there¬ 
fore, made of fine wire, so that a great many convolu¬ 
tions can be used, each one adding its own influence to 
the combined magnetic effect, while its own resistance 
{which, considered by itself, is great) is yet so small in 
proportion to the entire circuit that it does not decrease 
the strength to any great extent. 

The rule relating to the proper proportion of the 
electro-magnet to the circuit holds good in this case. 
For example, we have a line, two hundred miles long, of 


ELECTRO-M AGNETISM AND ELECTRO-MAGNETS. 57 

No. 9 wire, and a battery of eighty Callaud cells. We • 
are to have five relays. What should be the resistance 
of each of those relays \ 

“ We call the line-wire resistance 16 ohms per mile; 
then for 200 miles the line resistance will be 3,200 
ohms. Calling the battery resistance 3 ohms per cell, 
the resistance of the entire battery will be 240 ohms, 
giving as the total resistance of line and battery 3,440 
ohms. Then, following the rule already given, we must 
make the total resistance of the electro-magnets 3,440 
ohms also. This divided by 5, for the number of mag¬ 
nets, gives as the resistance of each magnet 688 ohms. 

In practice, however, as has already been observed, it is 
well to keep the magnet resistance less than that of the 
line and battery, to allow for variations in resistance 
due to weather. Moreover, in this country, for unifor¬ 
mity, the resistance of the majority of relays used is 
made very much the same for comparatively long and 
short circuits. 

“The condensed reason, then, why we use fine wire— 
and a great deal of it—for circuits of high resistance, is 
that the high resistance of the circuit greatly enfeebles 
the current, and we must use fine wire to make the best 
of the remaining strength of the current by a greatly- 
increased number of convolutions.” 

64. When ice require an electro-magnet for long lines , or for 
circuits of great resistance , why do ice call for one of high re¬ 
sistance i Is high resistance advantageous % 

No. Resistance, considered by itself, is a positive dis¬ 
advantage, because every additional unit of resistance 
added to the circuit tends to further enfeeble the cur¬ 
rent. But, as already stated, to make the most of the 
existing current we require many turns of wire, and the 
resistance is a necessary but unwelcome adjunct. If we 
could obtain the convolutions without the resistance it 
would be so much the better, but that is impossible ; 
and it has been found convenient to designate magnets 


58 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

intended to work on long lines as kigli-resistance mag¬ 
nets—not because it is in virtue of tlieir higli resistance 
that they work better, but simply because they necessa¬ 
rily have a higli resistance, and to denominate them as 
such is an easy way to distinguish them. 





CHAPTER VI. 


MAGNETO-ELECTRICITY, AND MAGNETO AND DYNAMO- 

ELKCTRIC MACHINES. 

» 

65. What is magneto-electricity l 

It is the name given to electric currents which are 
developed by the relative movements of magnets and 
wires. For example, if a magnet and a coil of insulated 
wire are caused to alternately approach and recede from 
each other rapidly, momentary currents are induced in 
the coil, which are alternately opposed to each other in 
direction. The process of developing magneto-electri¬ 
city, as already stated (see answer 18), is called mag¬ 
neto-electric induction. 

It is one of Faraday’s most important discoveries. 



While experimenting in the year 1881, he ascertained 
that by inserting the end of a permanent magnet into 
the middle of a coil of wire to which no battery was 

59 






























60 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

attached a current of electricity was produced, whose 
direction depended upon the pole of the magnet inserted 
and the direction in which the coil was wound. By in¬ 
serting the other end of the magnet a current in the 
opposite direction was produced. 

In the same year he produced a spark, a , b , by pulling 
an armature, s (covered with a coil of insulated wire, ri), 



Fig. 26.—The Electric Spark obtained from a Magnet. 

from the poles, N, S, of a magnet (Figure 26), and also 
obtained magneto-electric currents by rotating a copper 
plate between the poles of a magnet, and by sliding a 
coil of insulated copper wire upon a bar magnet. We 
see, therefore, that by the mere motion of a magnet in 
near proximity to a conductor, or of a conductor in the 
immediate vicinity of a magnet, without any battery, 
dynamic electricity may be produced. In the next year, 
1832, the first magneto-machine was invented, and elec¬ 
tricity generated in this manner is now one of the most 
important agents in the useful arts, and is for many pur¬ 
poses to be preferred to that produced by voltaic bat¬ 
teries. 




















MAGNETO-ELECTRICITY, ETC. 61 

66. What are the principal applications of magneto-electri¬ 
city i 

It has been extensively applied in ways too numerous 
to recapitulate. The following are, however, a few of 
its most important applications : 

Magneto-currents generated by small machines are 
frequently used for medical purposes, and have also 
been much employed in the experimental room and 
laboratory for chemical and physiological reactions. 

It is now almost universally used in the production of 
the electric light, and was first employed for that ob¬ 
ject by F. H. Holmes, who showed a machine for the 
purpose in the International Exhibition of 1862, since 
which time whenever the electric light has been profita¬ 
bly used, its currents have been generated by magneto- 
machines. 

For blasting, and the explosion of mines and sub¬ 
marine charges, it has proved a very valuable agent, 
Professor Wheatstone having devised an ingenious ap¬ 
paratus for the ignition of fuses. It has the power 
of igniting from two to twenty-five fuses simultane¬ 
ously. 

The application of magneto-electricity to electro-plat¬ 
ing was an event of importance in the history of that 
art. It was first so applied in 1842, and the machine 
then introduced was used for many years, but has now 
been superseded by newer and more improved arrange¬ 
ments, such as the Gramme, Weston, or Siemens and 
Alteneck machines. 

One of the most important applications of magneto- 
electricity is to telegraphy. Gauss and Weber, in 1833, 
moved their telegraph needle by magneto-electricity, 
which was the first employment of Faraday’s discovery 
in such service. 

Subsequently Steinlieil in 1837, and Wheatstone in 
1840, made great improvements in apparatus ; and at 
the present time Wheatstone’s alphabetical telegraph 
is almost exclusively employed on country lines in Eng- 


62 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


land, while the magneto-pointer telegraph of Siemens 
and Halske holds its own as a private-line instrument 
in Russia and Germany. In our own country the mag¬ 
neto-printers of G. L. Anders are well and favorably 
known. 

The magneto-current has been more extensively em¬ 
ployed during the last few years than ever before, owing 
to the extraordinary number of magneto-bells manufac¬ 
tured and introduced as telephone signals. The tele¬ 
phone itself is also an important application of magneto- 
electricity, which will be more fully considered here¬ 
after. 

A few years since an attempt was made by J. B. 
Fuller, of Brooklyn, N. Y., to work the Morse telegraph 
lines of the Western Union Telegraph Company by 
means of a dynamo electric machine. On account of 
the high speed necessary at that time to produce a 
uniform current this experiment was unsuccessful and 
was soon abandoned. 

In 1880 Stephen D. Field, of New York, renewed the 
experiment with improved apparatus and with a dif¬ 
ferent arrangement of circuits. He used three ma¬ 
chines, two of which had their armature coils in the 
circuits to be operated, while the third machine served 
to energize the field magnets of the first two. 

These later experiences have realized such a saving in 
the cost of electric power as to encourage high hopes of 
the profitable substitution at an early day of machine 
currents for voltaic electricity at many of the principal 
telegraph offices. 

67. Has the magneto-electric system of developing electricity 
any advantages over the voltaic-battery method t If so, describe 
some of them. 

For certain purposes it has decided advantages, some 
of which may be enumerated as follows : 

On comparatively short telegraph lines, such as pri¬ 
vate and municipal telegraphs, it is far superior to the 
battery system, inasmuch as although the first cost of 


M AG N ET0 - ELECTRICITY, ETC. 


63 


the machine is greater, there is practically no outlay for 
its management and maintenance, while the expense and 
annoyance inseparable from the maintenance of batter¬ 
ies are totally dispensed with. 

It lias also been ascertained, in the practical working 
of magneto-telegraphs, that they will work satisfactorily 
over a heavy escape that renders a line worked by bat¬ 
teries totally inoperative. 

In the production of the electric light the magneto- 
machine presents great advantages on the score of econ¬ 
omy and convenience. It has also been the most valu¬ 
able agent in bringing the cost of the light within com¬ 
mercial requirements. 

The chief objection to the use of the electric light was 
formerly the enormous expense necessarily contingent 
on the continued use of large voltaic batteries, and the 
consumption of zinc and other materials essential to 
keep them in good working order. 

The introduction of the magneto-machine in 1862 by 
Holmes, and the successive improvements that have 
.since been effected by Wilde, Siemens, Wheatstone, 
Ladd, Gramme, Weston, and others, have completely 
obviated this objection and made the electric light an 
ordinary illuminator, known and valued by many, in¬ 
stead of being, as formerly, a cabinet curiosity, only 
within the grasp of the professional electrician. 

These machines have also, with excellent results, been 
applied to electro-plating and electrotyping, and for that 
service are now being universally preferred to batteries, 
with the same advantages as in their application to 
lighting. This application of magneto-electricity was 
first made in 1842 by J. S. Woolricli, who took out a 
patent for the use of a magneto-electric machine in elec¬ 
tro-plating. The modern machines of Wilde, Gramme, 
Siemens and Alteneck, and Weston have, however, en¬ 
tirely superseded the Woolricli machine, and are now, 
in some of their multitudinous types, constantly used. 
The first Gramme machine used for this purpose ran 


64 ELECTRICITY, MAGNETISM, AND TELEGRAPHY'. 

five years without repairs or outlay, except the cost of 
oil for lubrication. 

But since the general introduction of the telephone 
magneto-electricity may be said to have found its appro¬ 
priate sphere. Merely mentioning the telephone itself, 
in which the magneto currents may be said to be invol¬ 
untarily generated, it was early seen that some signal 
was necessary to attract the attention of the distant 
telephone operator ; and the application, in a branch 
circuit, of the magneto-electric generative apparatus, in 
combination with the special polarized armature invent¬ 
ed by Thomas A. Watson, answered the purpose so ad¬ 
mirably that it is still used substantially in the same 
manner as at first. 

Many thousands of these bells are now in use, and 
will be fully described in their place. The use of the 
magneto-bell for a signal has also the advantage of 
being able to ring over long or short lines indifferently, 
and in large offices the economy in maintenance, and the 
valuable space saved which would otherwise be devoted 
to large batteries, is such a consideration as to render 
the magneto system the only one now regarded as worth 
a second thought. 

68. What is a magneto-electric machine t 

A magneto-electric machine may be briefly defined as 
an apparatus whereby motion is by means of magnetism 
transformed into electricity. Such machines are made 
in many different forms, and the modifications of the 
machine are almost as numerous as are those of the vol¬ 
taic battery. Nearly all may, however, be comprehend¬ 
ed in three classes : 

First. Those in which the working current is gene¬ 
rated by the movement of coils of wire in the vicinity 
of permanent magnets. 

Second. Those in which a comparatively small perma¬ 
nent magnet and armature are made to generate a cur¬ 
rent which is merely made use of to excite a very large 
electro-magnet. This is then used to induce a second 


MAGNETO-ELECTRICITY, ETC. 


65 


current, which can be as much stronger than the first as 
the electro-magnet is more powerful than the permanent 
magnet. 

Third. Those in which the small amount of residual 
magnetism always present in electro-magnets is utilized 
to generate a current, which is first used to increase the 
magnetism of its inducing magnet and thereby its own 
strength. When the current reaches the required point 
of strength, in some of the machines of this class, a por¬ 
tion is shunted off for use, while another portion is di¬ 
rected continuously through the coils of the inducing 
magnet, thereby maintaining its magnetism. 

In other machines the whole of the current generated 
in the armature-coil is led through the magnet-coil be¬ 
fore passing out to the external circuit. 

Each of these three classes may be again subdivided 
into machines furnishing alternating and machines fur¬ 
nishing direct or continuous currents. 

69. Describe a machine of the first class mentioned. 

This class of machine is the simplest of any, and for 
a long time was the universal type of all magneto-ma- 



Fig. 27. 

chines in use. It is shown in Figure 27. A pair of 
coils, c d , of insulated wire, connected together in the 














































66 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


same way as electro-magnets, contain soft-iron cores, a b , 
united by a soft-iron yoke-piece, X; these are fixed on 
a horizontal axis, S, which may be revolved rapidly by 
means of a cord passing over a multiplying-wheel, W, 
and a pulley on the axis S, in front of the poles of a 
permanent magnet or series of magnets, M. The rapid 
alternate approach and retreat of the coils through the 
magnetic held of the permanent magnet induces cur¬ 
rents in each coil, which, by means of a circuit-breaker, 
Jc i, dipping into a mercury bath having two chambers, 
l m, insulated from one another, are made intermittent, 
and thus shocks may be received from the handle-con¬ 
ductors, H H. 

Dispensing with the circuit-breaker, the currents may 
be led oft* by suitable conductors. For some purposes, 
such as ringing bells, these reversed currents are used 
just as they come from the machine ; but if the current 
is required to be continuous and to how in the same 
direction constantly, as it necessarily must for many 
purposes, an arrangement called a pole-clianger or com¬ 
mutator is attached to the axis of rotation and to the 
terminals of the coils, which brings both currents into 
the line in the same direction. The commutator, one 


form of which is re¬ 
presented in Figure 
28, is an attachment 
on the armature-sha ft, 
by which the two 
leading-out wires are 
reversed at the same 
instant that the cur- 



Fig. 28. 


rents are ; so that, on the well-known principle that two 
negatives are equivalent to an affirmative, the current 
reversal does not become apparent. 

The above remarks do not refer to machines working 
upon the principle of the Gramme machine, since such 
machines originate a constant current in one direction. 

Machines of the class just described may, and now 




MAGNETO-ELECTKICITY, ETC. 


67 


often are, provided with a Siemens armature instead of 
the two helices fixed upon the soft-iron cores and yoke- 
piece. 

70. What ivas the first important advance made in magneto- 
machines after the invention of those already described t 

The invention of the Siemens armature. It was pro¬ 
posed in 1857 by Dr. Werner Siemens, and consists of a 



cylindrical piece of soft iron hollowed out at two sides 
for the reception of insulated wire wound longitudinally 
or parallel to its axis. 

This armature is shown in Figure 29 ; No. 1 represent¬ 
ing a side view, No. 2 the coiled armature, and 3 an 
end view thereof. In No. 1 G shows the hollowed sides 
before winding. In No. 2 L L is the commutator; 
H II brass bands which bind securely the bands of 
covered wire ; I I are the axles on which the armature 
revolves, and K a pulley for a driving-belt. This ar¬ 
mature is fixed on bearings in a magnetic cylinder 
formed by the extension of the poles of the permanent 
or electro magnet, which are joined together by brass 
or copper strips. 

The Siemens armature is rapidly revolved within this 
chamber, and from its position directly between the 
poles of the magnet, where the magnetic field is much 
more intense than in that occupied by the old form of 
armature, much more powerful currents are produced. 
The terminals of the wire wound round the armature 
are led out of the chamber and convey the current to 
its desired destination. 







































































68 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


71. Describe a machine of the second class which illustrates the 
second great improvement. 

The machine which may be regarded as the type of 
the second class is that of Henry Wilde, of Man¬ 
chester, England, who discovered that if the current 
produced by the revolving armature of a permanent 
magnet was made to flow through the coils of an elec¬ 
tro-magnet, a degree of magnetism much stronger than 
that of the original magnet, was produced by revolving 
the armature sufficiently fast. 

Having made this discovery, it then occurred to him 
that an electro-magnet so excited might be used to 
evolve a proportionately large amount of electricity. 
Making a machine embodying the principle, he discov¬ 
ered that such was the case. The following is a descrip¬ 
tion of the Wilde machine, as patented by him in 1867 : 

A very large electro-magnet, A B, of the horseshoe 
pattern, forms the lower and much larger part of the 
machine, and is fixed with its poles downward; the 
yoke-piece joining the two electro-magnet cores is util¬ 
ized as a base whereon to place a series of permanent 
magnets, M, also having their poles downward. 

The permanent magnets are much smaller than the 
electro-magnet. Both magnets are provided with Sie¬ 
mens armatures, which are rapidly revolved simulta¬ 
neously by the same power. The armatures rotate in 
what is called the magnet-cvlinder. 

This, in the upper cylinder, is formed by masses or * 
pole-pieces of iron, m n , and in the lower by similar 
pole-pieces, T, attached to the poles of the magnet, and 
kept separate from each other by brass or copper plates, 
o and i ; these are bored to make a cylindrical cavity. 

The upper armature is rotated with a velocity of about 
twenty-four hundred revolutions per minute, and the 
current thereby obtained is directed, after passing 
through a commutator, to binding-screws, p and q, and 
thence through the coils of the electro-magnet below. 
These currents maintain the electro-magnet in a state of 


MAGNETO-ELECTRICITY, ETC 


69 


powerful magnetization, and the currents induced in its 
revolving armature are much more powerful than those 
of the exciting magneto-machine, and are utilized in the 
work done external to the machine. With such a ma- 



irpmnnpi 


[illiiiiiiiim 


chine an iron rod fifteen inches long and one-fourth of an 
inch thick was melted. 

72. Describe generally the machines of the third class which 
include the third great improvement. 

The principle on which the third class of machines 



















































































































































70 ELECTKICITY, MAGNETISM, AND TELEGRAPHY". 


is based was first patented in 1854, in England, by Soren 
Hjorth, of Copenhagen, wlio was indisputably its first 
discoverer, and also the first inventor of a machine 
whereby the said principle Avas made operative. 

In December, 18G6, the same principle was redis¬ 
covered and repatented by S. Alfred Yarley, and in 
February, 1807, was communicated to the Royal Society 
by Professor Wheatstone and by Werner Siemens, each 
of these gentlemen having independently made the dis¬ 
covery, while neither of the latter appear to have known 
anything of the prior patent of Hjorth. 

This principle is, briefly stated, “ that electro-magnets, 
after being once magnetized, always retain a little mag¬ 
netism ; and that if the generating armature-coil of a 
magneto-electric machine be placed in circuit with the 
wire forming the helices of the inducing magnets, or if 
the latter are arranged to form a derived circuit with 
the circuit of the armature-helices, when the armature 
is rotated, infinitesimal currents are generated by means 
of the initial weak magnetism. These circulate round 
the helices of the inducing magnets and increase their 
magnetism, causing the production of stronger currents. 
These currents are again sent round the inducing mag¬ 
net-helices, strengthening the magnetism still more; it 
again reacts on the armature, this mutual give and take 
continuing until the inducing magnets become satu¬ 
rated with magnetism, when the currents generated are 
of great power. 

It must be understood that this principle of mutual 
accumulation is applicable to all machines provided with 
electro field-magnets. Nearly all the best and most 
powerful machines now constructed are arranged upon 
this principle ; for example, those of Brush, Siemens and 
Alteneck, Gramme, Weston, Edison, Maxim, and others. 
One of the first machines made embodying the principle 
was that of Ladd; and a general description of Ladd’s 
machine will suffice for all, as, although each machine 
has different details of construction and arrangement, 


71 


MAGNETO-ELECTRICITY, ETC. 

tlie method of applying tlie accumulative feature is sub¬ 
stantially identical in all. 

Ladd s machine consists of two parallel electro-mag¬ 
nets, BE' A Siemens armature, M, is placed at each 
end. 1 hey are, however, of different sizes. The smaller 
one is in circuit, by means of wires p n, with the coils 
of the electro-magnet, and the larger one furnishes the 
woiking current, which, by wires p' is led wherever 
desiied. ilie two armatures are revolved simultane- 



Ffe. 81. 


ously. The current is at first generated in the coils of 
the smaller armature by the residual magnetism of the 
electro-magnets. This armature, as it revolves, sends 
the currents generated in its coils through the coils of 
the magnet. The magnetism thus increased magnifies 
the currents induced in the revolving coils, and at the 
same time develops powerful currents in tlie larger 
armature, thus carrying on the principle of mutual ac¬ 
cumulation. The current developed in the larger arnia- 














































































72 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

ture is utilized for the purpose desired, which in the 
figure is represented as an electric-light, I. Ladd’s ma¬ 
chine is really a combination of the ideas of Wilde 
with the principle of accumulative action. 

73 . What is the principle and general construction of the 
Gramme and other ring-armature machines f 

The Gramme, Brush, Wallace Farmer, and all ma¬ 



chines using the ring-armature, have for their vital 
principle the simple fact of the substitution of the soft- 
iron ring for the rotating-shuttle armature of other ma¬ 
chines. The ring armature was first proposed in 1860 
by Dr. Pacinotti, of Italy ; but not until 1870, when re- 





































































































































73 


MAGNETO-ELECTRICITY, ETC. 

invented and brought into use by Z. T. Gramme, was its 
utility recognized. 

Its peculiar armature enables the Gramme and the 
numerous machines based thereon to evolve a continu¬ 
ous current in one direction without the necessity of 
employing a commutator, properly so-called. Instead 
of this the coil terminals are formed into a collector , as 
hereafter described. 

The soft-iron ring is endless, and the insulated wire 
with which it is 
wrapped, and 
in which the 
electricity is 
induced, is also 
endless. 

The wire is 
put on in sepa¬ 
rate coils, and 
the in-wire of 
one coil united 
to the out-wire of the next. But from each of these 
junctions between any two adjacent coils a branch wire 
is led to a metal plate on the axis of rotation of the 

ring. The metal plates 
which connect with tliese 
branch wires are symmet- 
ricallv arranged round 
the axis, all insulated 
from one another, as 
shown in Figure 34, and 
metal brushes or springs 
press upon them at each 
side, nearly at right an¬ 
gles to the magnet poles ; 
one of the brushes con¬ 
necting with one of the 
leading-out wires, and the other with the second lead¬ 
ing-out wire. 













74 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


The operation of the ring is as follows : All the coils 
which at any given' moment are in the semicircle on 
either side of one of the magnet poles—see Figure 33— 
say the north, are, when the ring is rotated, traversed 
by a current of one direction ; and as these coils are all 
joined together in series, the current in one traverses all. 
Similarly, the semicircle formed by the coils imme¬ 
diately approaching, or immediately receding from, the 
south pole are at the same time traversed by a current 
of opposite direction. So long as the leading-out wires 
are open these currents have no outlet, and conse- 
quentl} 7 oppose and neutralize one another. But if we 
close the external circuit the two currents, one on each 
side of the ring-coils, operate in the same way as a pair 
of batteries connected in multiple arc, both uniting in 
the same direction and issuing from the ring-coils to¬ 
gether, giving to the brush on one side of the ring the 
effect of a plus pole, and to the other that of a minus 
pole, of a battery, the result being a continuous and 
non - al t erna ting cu rren t. 

It may be noted that the collection of metal plates 
ranged round the axis and forming the coil terminals is 
frequentlv but erroneouslv called the commutator. 

74 . What are the chief peculiarities of the Brush machine t 

In it the ring-armature is made of cast-iron, and lias 
its two flat surfaces divided into as many deep rectan¬ 
gular grooves as there are coils of insulated wire to be 
carried by the ring. 

The ring itself is deeply grooved in its periphery, and 
the projecting sides which form the grooves are also 
grooved concentrically. These grooves serve to dimin- 
ish the mass and weight, and also to ventilate the ring, 
to carry away a portion of the heat which generates 
during rotation, and to prevent and neutralize local cur¬ 
rents of electricity which would otherwise operate 
against the efficiency of the machine. The armature- 
coils are wound in the rectangular grooves until the 
outermost convolution becomes flush with the sides of 


Fig. 35.—The Brush Machine 









































































































































































76 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


each groove. Thus when tlie ling rotates the side of 
each coil is caused to pass very close to the poles of the 
field-of-force magnets. 

The coils work in pairs, the inner wire of one coil 
being united to the inner-wire end of the coil which is 
immediately opposite to it. 

All the outer ends are led through the central shaft, 
which is hollow, and terminate in a commutator, which, 
operates to cut out the two coils of a pair at the moment 
when they are passing the neutral point of the magnetic 
field and are not generating any current; this reduces 
the resistance of the machine when working. The cir¬ 
cuit of any two of the coils thus cut out is also opened 
by the commutator, so that no current can circulate in 
them. The current is taken from this collecting com¬ 
mutator by suitable brushes, and the Brush machine, as 
well as those of the Siemens type, collect their currents 
by a system of coil terminals similar to that of the 
Gramme machine. 

75. What is meant by the term “ clynamo-electric machine 
and in wliat does such a machine differ from a “ magneto-elec¬ 
tric mach ine ” i 

The term dynamo-electric has by common consent 
come to be exclusively applied to machines which are 
here placed in the third class described—namely, those 
in which the current is developed in the first place by 
the residual magnetism (which is never entirely absent 
from the iron core of an electro-magnet that has once 
been magnetized), and in which the current so devel¬ 
oped is passed through the coils of the developing elec¬ 
tro-magnet, thus increasing its magnetism, and, as a 
consequence of the increased magnetism, increasing also 
the current developed by it, the machine continually 
increasing its action, as it were, at compound interest 
up to a certain point, where the work of bringing the 
armature past the poles becomes so difficult as to bal¬ 
ance the driving power. 

The term dynamo-electric is also occasionally made to 


MAGNETO-ELECTRICITY, ETC. 77 

include machines of the second class, such as Wilde’s, 
and, strictly speaking, is applicable to any form of ma¬ 
chine (including even those which develop frictional 
electricity) by which work is transformed into elec- 
tricity. 

Many writers have explained the term dynamo-elec¬ 
tric by stating that sncli a machine is one in which the 
held of force is produced by electro-magnets, in contra¬ 
distinction to those in which permanent magnets are 
used; the latter being termed magneto-electric ma¬ 
chines. 

It is obvious that this explanation is incorrect, ex¬ 
cept in so far as it conveys the idea that machines em¬ 
ploying permanent held magnets cannot be utilized on 
the mutual-accumulation plan. 

The following views, it is believed, will, if examined 
carefully, be found to be correct: 

First. All machines in which the electricity is de¬ 
veloped by moving a closed wire circuit through a mag¬ 
netic held of force, whether that held be produced by 
permanent or electro-magnets, or whether the magnetism 
be produced by self-developed electricity or by electri¬ 
city furnished by an external exciter, are true magneto- 
electric machines. 

Second. All machines by which energy in the form of 
moving power is transformed into energy in the form of 
electricity are properly called dynamo-electric machines. 

Inasmuch as these terms are almost universally ap¬ 
plied erroneously, it may be well to add other definitions 
as follows, so that the student may be fully informed 
not only as to the correct meaning of the terms, but also 
as to the incorrect but popular understanding: 

Dynamo-electric machines, according to the popular 
acceptation of the term, are those in which the reaction 
principle of mutual accumulation is employed. 

Magneto-electric machines are usually and popularly 
understood to be those in which the field of magnetic 
force is produced by permanent magnets only. 


78 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


Machines which excite their own field-magnets are of 
two general types—/.<?., those in which the field-magnets, 
armature, and external circuit are all united in one se¬ 
rial circuit, as shown in diagram in Figure 36 ; and those 



— 

A’ 

r 

i 

> 

) > 

r 

^_> 

> 

r". 

s 

<P 

) N 


__/ 

Fig 36. 



in which only a part of the current generated by the 
armature is passed through and excites the field-mag¬ 
nets, as diagrammatically represented in Figure 37. 
This form is coming into more extended use, having 
been first proposed by Wheatstone, and is known as 
the shunt dynamo. 




Machines of the character proposed by Wilde—viz., 
those in which the field magnets are energized by cur- 







































































MAGNETO - ELECTRICITY, ETC. 


79 


rents derived from an external source—are called sepa¬ 
rately-excited dynamos ; and the principle of arrange¬ 
ment is shown by Figure 38. Finally, to make clear the 
arbitrary distinction between so-called magneto-electric 
and dynamo-electric machines, and to show that it is 
more a matter of nomenclature than anything else, the 
former, or a machine in which the lield-magnets are of 
the permanent character, is represented by Figure 39. 

76 . For what purposes are constantly alternating currents 
used ichen produced by magneto or dynamo-electric machines i 

For printing or dial telegraphy, for signal bells in 
telephony, and for some systems of electric lighting, 
chiefly the Jabloclikoff candle system, and several of 
the British and French lighthouse lamps. 

77 . For ivhat purposes are magneto or dynamo-electric cur¬ 
rents of continuous direction chiefly employed i 

Principally for electric lighting, either by arc or in¬ 
candescence ; for electro-plating and electrotyping ; for 
the transmission of power, and for furnishing currents 
for long telegraph lines. 


CHAPTER VII. 

INDUCTION-COILS AND CONDENSERS. 

78 . What is an induction-coil , and ichy is it so called f 
It is an instrument designed to obtain electricity of 
great electro-motive force from a source of small elec¬ 
tro-motive force. It consists of a sliort coil of compaia- 
tively thick insulated wire, around which is wound a 
very long coil of line wire. In the centre of the coarse 
wire coil is placed a core of soft iron or a bundle of soft- 
iron wires. The thick wire coil is placed in circuit with 
a battery and circuit-breaker. 



Fig. 40.—The Induction-Coil. - 


In the figure K is a screw for turning the reversing 
commutator, L ; E is the body of the coil; M the soft- 
iron core, provided with a solid cap, e; D is the ham¬ 
mer of the circuit-breaker, X ; and Y and X are the 
terminals of the secondary coil. 

The induction-coil was invented by Professor Charles 
G. Page, of Salem, in 1836 ; brought to a state of great 
perfection in the shop of Ruhmkorff in 1851, and in 

1857 much improved by Ritchie, of Boston. It is both 

80 





















INDUCTION-COILS AND CONDENSERS. 


81 


a magneto-electric and an electro-magnetic apparatus, 
because tlie induced current which manifests itself at 
the terminals of the fine wire coil is formed by the con¬ 
junction of a magneto-electric current, caused by the 
rapid magnetization and demagnetization of the core as 
the voltaic current in the coarse wire coil is alternately 
made and interrupted, and of that excited in the fine 
wire coil by electro-dynamic induction from the coarse 
wire coil during the same.contacts and interruptions. 

To particularize: We have already seen (18) that 
when a closed circuit is in proximity to a conductor 
which is in connection with a voltaic battery, at the 
moment a current arises or ceases in that conductor an¬ 
other current of momentary duration arises also in the 
closed circuit near it. We have also seen that when a 
magnet is moved near a coil of wire, or a coil of wire 
near a magnet, a current is developed in the coil on the 
approach of the two, and another in an opposite direc¬ 
tion as they are parted. 

These effects are combined in the induction-coil, as 
the coarse wire coil performs two duties at the same 
time—namely : 1st. That of advancing and withdrawing 
the inducing magnet, which it does most effectually by 
alternately causing the soft-iron core in its interior to 
become magnetized and demagnetized. 2d. That of 
causing, by the make and break of its own circuit, 
momentary currents of electricity of rapidly alternat¬ 
ing direction. 

Thus we see that the voltaic induced currents are su- 
peradded to those induced by the core in its magnetiza¬ 
tion and demagnetization, to form the induced currents 
circulating in the fine wire coil. 

The instrument is called the induction-coil because the 
currents of the fine wire coil are produced solely from 
inductive causes; and the electro-motive force thus in¬ 
duced in a long coil is so enormously greater than that 
of its inducing battery as to assume an appearance very 
similar to that of frictional or mechanical electricity. 


82 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


79 . What is the primary circuit, ancl what is meant when we 
speak of a primary current f 

The pr imary circuit or coil is the coil of comparative¬ 
ly thick wire which is connected with a battery and cir¬ 
cuit-breaker. Within it is inserted the soft-iron core, 
and it is itself inserted within the coil of fine wire. It 
may also be called the main or inducing circuit, but the 
term primary circuit literally means u the first circuit.” 
It is called the primary coil because it is employed for 
the conveyance of the battery current. It will hereafter 
be understood that whenever the word primary is used 
with reference to induction-coils it is intended to signify 
the battery circuit. When we speak of the primary cur¬ 
rent we mean the battery current that traverses the pri¬ 
mary coil. It is sometimes called the inducing current. 


80 . What is meant by the terms secondary coil and secondary 
current t 

The secondary coil is the long coil of fine wire which 
surrounds the primary coil, and in which the moment¬ 
ary currents, induced by the primary coil and core, are 
developed. 

The wire of the secondarv coil is much longer and 
thinner than that of the primary. It is called the sec¬ 
ondary coil, both in contradistinction to the primary 
coil and because the currents set up in it are dependent 
entirely for their existence on the first or primary cur¬ 
rent, which circulates in the primary coil and excites 
magnetism in the core. 

As the induced currents are much more powerful than 
the primary currents, it is necessary to be much more 
careful in insulating the wire composing the coil. 

The secondary or induced current is the current or, 
more properly, the series of currents which are excited 
in the secondary coil by the rapid magnetization and 
demagnetization of the soft-iron corein conjunction with, 
and caused by, the make and break of the primary cir¬ 
cuit. This current has a much higher electro-motive 
force than the battery or primary current. 


INDUCTION-COILS AND CONDENSERS. 83 

81. TI licit is the circuit-breaker , and why is it necessary f 

In an induction-coil the circuit-breaker is the arrange¬ 
ment applied to the primary wire, which, forming part 
of the actual circuit, alternately completes and inter¬ 
rupts it. It is generally, in ordinary coils, automatic, 
or self acting ; for the soft-iron core is often made use 
of to work the circuit-breaker. 

An iron plate or armature is fixed to a flat spring, 
opposite one of the ends of the core, and, when not in 
operation, it presses against a metallic contact-stop by 
the elasticity of the spring. The circuit of the battery 
and primary coil passes through this armature-spring 
and contact-stop. For example: Starting from the posi¬ 
tive pole of the battery, the path of the current is first 
to the metallic contact or back stop; thence to the ar¬ 
mature and spring ; then to one of the primary coil 
terminals, through the coil, and from the other terminal 
to the negative pole of the battery. 

Now, when the battery is connected, to put the coil 
in operation the current passes through the primary 
coil and causes the core to become magnetic. The 
armature is then attracted to the core and away 
from its back contact. This breaks the circuit; the 
magnetism disappears; the armature, under the influ¬ 
ence of the spring, falls back, closing the circuit; this 
action of alternately establishing and breaking the con¬ 
tinuity of the primary circuit is repeated indefinitely. 

The rapidity of the vibrations is regulated by an ad¬ 
justing screw. The circuit-breaker is sometimes worked 
by a separate electro-magnet and sometimes by clock¬ 
work or other mechanical movements. In one form or 
another it is an indispensable adjunct to the induction- 
coil, because, as we have seen, the number of induced 
currents depend entirely upon the breaking and closing 
of the primary circuit, and the consequent change of 
magnetism in the core. 

If we close the primary circuit once, we merely get one 
pulsation of current in the secondary coil. If we then 


84 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

open the primary we again perceive but one pulsation 
in the secondary coil, but this time in the opposite di¬ 
rection. Hence, if we rapidly break and close the pri¬ 
mary circuit we see there is a corresponding succession 
of alternating currents in the secondary coil. 

82. What is meant by the extra current f 

It is the name given to a current set up in the primary 
coil by induction between the several convolutions of 
the same wire when a current is sent through it. It is 
produced both on making and interrupting the battery 
contact, but is much stronger when the circuit is bro¬ 
ken, because then the extra current is in the same di¬ 
rection as the primary currents ; but when the circuit 
is made the extra current is in opposition to the pri¬ 
mary current, which, as it were, arouses an opponent in 
its own path. Thus we see that the action of the pri¬ 
mary coil, in addition to inducing a current in the sec¬ 
ondary coil, also induces a current itself. This current 
is made apparent in the following manner : If we attach 
the two coils of a wire to a battery, and place a contact- 
breaker in circuit, a very fine spark will be observed on 
breaking contact. 

But if we wind the piece of wire into a helix or spiral 
we will at once notice that the spark is much larger 
and brighter. This is caused by the action of the ex¬ 
tra current, which, as previously stated, is on breaking 
contact, in the same direction as the battery current, 
and the spark is the combined effect of the two cur¬ 
rents. 

The extra current caused when contact is made is 
called the inverse current; when caused by breaking 
contact it is called the direct current. The phenome¬ 
na caused by the extra current were first noticed by 
Professor Joseph Henry in 1832. It was subjected to 
experiment by Faraday in 1834, who proved that botli 
the spark and shock given on breaking contact were 
due to this cause. 

In order to overcome the injurious effects of the ex- 


INDUCTION-COILS AND CONDENSERS. 85 

tra current the circuit-breaker is frequently bridged or 
looped by a condenser. By thus bridging the circuit- 
breaker the iron is demagnetized with greater rapidity^ 
und the spark is also considerably lessened. 

The extra current of breaking contact enters the con¬ 
denser, and accumulates on its plates instead of jumping 
across the points of the circuit-breaker in the form of a 
spark; one of the condenser-plates being charged plus 
and the other minus. As the current flows from one 
terminal of the helix to the other, one end will draw 
plus electricity from, and the other add plus electricity 
to, the condenser-plates. When the circuit is again 
closed the charge in the condenser aids the battery cur¬ 
rent, because its discharge coincides with the direction 
of the battery current, and therefore the opposing force 
of the extra current is lessened by the combined forces 
acting against it. 

83. What is a condenser i 

It is an arrangement of conducting-surfaces by which 
a great quantity of electricity can be accumulated upon 
a comparatively small area. 

It is based upon the law that “ the capacity of a con¬ 
ductor is greatly increased when it is placed near to an¬ 
other conductor charged with the opposite kind of elec¬ 
tricity.” Any apparatus which consists of two good 
conductors, which are separated from each other at a 
small distance by a non-conductor, may properly be 
called a condenser. 

A Leyden jar, therefore, which usually consists of two 
tinfoil surfaces separated by a dielectric of glass, con¬ 
stitutes a condenser. 

As usually constructed for use in telegraphy or in 
connection with induction-coils, the condenser consists 
of alternate layers of tinfoil and paper saturated with 
paraffine. Each alternate metal plate is connected so as 
to form two distinct series, insulated from each other by 
the interleaved sheets of paraffined paper. The two se¬ 
ries of plates are each united to binding-screws which 


86 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


form the terminals of tlie plates and may be connected 
in any desired way ; as, in the induction-coil, one termi¬ 
nal is connected with one side of the circuit-breaker, and 
the other terminal with the other side of the same. It 
is usual to represent a condenser by the conventional 



Fig. 41. 


sign of a series of thin lines interleaved with one an¬ 
other, as in Figure 41. 

84. Why is a soft-iron core inserted within the primary coil t 

Because, in the first place, without it the current pro¬ 
duced in the secondary coil would be caused solely by 
dynamic induction from the battery current circulating 
in the primary coil, and in that case would be compara¬ 
tively weak ; while when the core is inserted it is alter¬ 
nately magnetized and demagnetized by the rapid make 
and break of the battery circuit, and so induces a mag¬ 
neto-electric secondary current, which adds its etfect to 
that of the current caused by the voltaic or dynamic in- 
duction. and makes the combined effect very strong and 
intense. In the second place, the soft-iron core is often 
utilized as an electro-magnet, and in that capacity is 
made to attract the contact-breaker, thus effecting by 
its own magnetism the rapid interruptions of the bat¬ 
tery current. 

As it is important for the proper operation of an in¬ 
duction-coil that the core shall gain and lose its mag¬ 
netism very quickly, it is usually composed of a great 
number of unpolished soft-iron wires, which are partly 
insulated one from another by a thin coating of oxide. 






















INDUCTION-COILS AND TELEGRAPHY. 


87 


The circulation of induced currents in the substance of 
the iron is thus prevented. 

85. Give a brief description of some of the largest induction- 
coils which have been made. 

The coil made by Ritchie, of Boston, for Mr. Gassiot, 
is one of the most powerful instruments constructed. 
The primary coil is of No. 9 wire, Birmingham gauge, 
and is wound in three layers, the length being 150 
feet. This coil has a gutta-percha case, over which is 
placed a glass tube. Over this again is arranged the 
secondary coil, divided into three sections, each five 
inches long, and wound on glass cylinders. The total 
length of the secondary wire is 73,650 feet, or nearly 
fourteen miles, and the core consists of a bundle of soft- 
iron wires, the bundle being eighteen inches long and 
about an inch and three-quarters in diameter. The 
contact-breaker is worked by a ratchet-wheel turned 
by hand. This coil, with five cells of Grove battery, 
has given sparks twelve inches and a quarter long. 

Ritchie lias since constructed a coil for the Stevens 
Institute of Technology which lias a primary coil made 
of No. 6 wire and 195 feet long. The core is a bundle 
of No. 20 iron wires, and the secondary wire is more 
than 50 miles long and is made of No. 36 wire. It lias, 
using 3 large bichromate cells, given sparks 21 inches in 
length. 

The largest coil made is that of the Polytechnic In¬ 
stitute, London. Its primary coil weighs 145 pounds 
and is 11,310 feet long, while the secondary wire is 150 
miles long, weighs 606 pounds, and has a resistance of 
33,560 ohms. The core is a bundle of No. 16 iron wires, 
and as a whole is 5 feet long and 4 inches in diameter. 
The entire instrument is 9 feet 10 inches long and 2 feet 
in diameter. This coil has given sparks 29 inches in 
length. 

Perhaps, however, the most wonderful machine of 
this class is that constructed by Mr. Apps, of London, 
for Mr. Spottiswoode, of the Royal Society. It is capa- 


88 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


*• 


ble of producing sparks 42 inches in length. It lias two 
primary coils, which can be readily substituted for each 
other. One is intended for the production of long 
sparks, the other for short and thick sparks. The 
secondary coil consists of 280 miles of wire. Its resist¬ 
ance is 110,200 ohms ; and the total number of con¬ 
volutions is 341,850. The first primary coil is 990 feet 
long, has a resistance of 2^ ohms, consists of 1,344 turns 
in 6 layers, and weighs 55 pounds. It lias a core con¬ 
sisting of a bundle of iron wires, forming together a 
core 44 inches long, upward of 3J inches thick, and 
weighing 67 pounds. 

86. What are the uses of the induction-coil f 

It is a valuable agent in chemical and physical re¬ 
search ; has been used in mines to furnish electric light 
in hermetically-sealed tubes, and also, in the place of 
the frictional machine, to charge Leyden jars. It is ex¬ 
tensively employed for medical purposes, and has by 
Siemens and Halske been applied to telegraphy. For 
gas-lighting it has been very useful, and, last but not 
least, has been successfully adapted to battery tele¬ 
phones. 


CHAPTER VIII. 


DEFINITIONS OF ELECTRICAL PROPERTIES, TERMS, AND 

UNITS. 

87. IT licit is the meaning of the term potential when used 
in electrical science f 

Potential is a word which literally means power to do 
work, and is nsed to denote the electrical condition of 
any body, or the degree to which that body is electri¬ 
fied. 

As we shall hereafter see, a large quantity of electri¬ 
city imparted to a conductor of small capacity will elec¬ 
trify it up to a very high potential. The higher the 
potential of any electrified body the greater is its ten¬ 
dency to pass to a point of lower potential, and con¬ 
sequently the greater its power to do work or overcome 
resistance in so passing. We find that it is customary to 
refer to positivelj r electrified bodies as being electrified 
to a high potential, and to bodies which are negatively 
electrified as having a low potential. 

Precisely as we take the level of the sea as a zero- 
point in measuring the altitude of mountains or the 
depth of mines, so we take the electrical condition of 
the surface of the earth and assume it to be the poten¬ 
tial zero-point, all bodies positively electrified having a 
higher potential than the earth, and all bodies negative¬ 
ly electrified being assumed to have a lower potential 
than the earth ; thus the potential of any other body is 
the difference between the electrical condition of the other 
body and the earth. No body can be said to have an 
absolute potential, but for brevity the word is used by 
itself to signify the difference ; precisely as, speaking 
of a Fahrenheit thermometer, we would say, “The de¬ 
gree of heat is 60 degrees,” meaning thereby 60 degrees 

89 


90 ELECTRICITY, MAGNETISM, AND TELEGRAPHY”. 

above zero. The meaning is practically the same as 
the word tension , generally used in the older text-books 
of electricity. 

Whenever electricity moves, or tends to move, from 
one place to another, there is said to be a difference of 
potential between those two places. 

The place from which the positive electricity tends to- 
move is assumed to be of higher potential than the 
other. The difference of potential between any two 
points expresses the amount of work which each unit 
of the electricity could do on its journey if it could all 
be utilized to do work instead of having to overcome the 
resistance of a circuit. 

In a voltaic battery the difference of potential be¬ 
tween the two ends of the battery is always maintained 
by chemical energy or work, and therefore the flow of 
current keeps up indefinitely ; for so long as the plates- 
of the battery are at opposite potentials, so long the cur¬ 
rent must continue. 

88. What is meant by electro-motive force t 

The term electro-motive force means that property of 
any source of electricity by which it tends to do work 
by transferring electricity from one point to another. 

For the sake of brevity it is frequently written E. M. F. 
It is produced by difference of potential, and in prac¬ 
tice may often be considered to be the same property. 
‘‘Just as in water-pipes a difference of level produces a 
pressure, and the pressure produces a flow so soon as 
the cock is turned on, so difference of potential produces 
electro-motive force, and electro-motive force sets up a 
current so soon as a circuit is completed for the electri¬ 
city to flow through.” * 

The electro-motive force of a battery is the power 
which it has of overcoming resistance. It increases in 
direct proportion to the number of cells employed—ten 
cells having exactly ten times the electro-motive force of 


* “ Electricity and Magnetism,” S. P. Thompson. 


DEFINITIONS OF ELECTRICAL PROPERTIES, ETC. 91 

one cell—but is not in any way dependent on tlieir size, 
since a cell as small as the bowl of a tobacco-pipe pos¬ 
sesses as great an electro-motive force as a cell of the 
same materials which would hold a gallon. The electro¬ 
motive force of the Daniell battery in volts is 1.079 ; 
and that of most of the copper-sulphate forms, about 
the same. The Grove is 1.950, chromic acid 2.028, Le- 
clanche 1.481, and the Smee, when in action, 0.482. 

89. What is the meaning of the term resistance f 

It has been already stated that some substances pos¬ 
sess the property of allowing electricity to diffuse itself 
freely and readily through them, and are therefore call¬ 
ed conductors , while others offer much opposition or re¬ 
sistance to this diffusion, and are hence called non-con¬ 
ductors or insulators. These terms are not absolute, as 
even the best conductors offer some obstruction to the 
passage of the current, and the best insulators will in 
some measure conduct electricity. Resistance, then, is 
the name given to this obstruction which is offered to 
the passage of the current by the substance of the cir¬ 
cuit through which it passes ; and when it is very great 
it becomes insulation. It is a property of every sub¬ 
stance, and in each substance differs in degree, from sil¬ 
ver, which offers the least resistance to the current, to 
gutta-percha or india-rubber, which offer a very great 
resistance indeed. 

In a telegraph line the total resistance is composed 
of the resistances of the line wire, the earth, the instru¬ 
ments, and the internal resistance of the battery. 

The resistance of any given wire increases in exactly 
the same proportion as the length of wire is increased ; 
for instance, fifty miles of No. 12 wire offer exactly 
fifty times the resistance of one mile. It also decreases 
in proportion as the area of the cross-section is in¬ 
creased ; for example, a wire one mile in length, with 
a cross-section having an area of a square inch, offers 
just one-fourth the resistance of a wire the same length 
whose sectional area is one square half-inch—because 


92 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

the square half-inch is contained just four times in the 
square inch. 

To make the idea as plain as possible, the resistance 
of a wire increases with increased length, keeping the 
gauge the same, and decreases with increased weight, 
keeping the length the same. Resistance may be de¬ 
fined as that quality of a conductor by which the 
strength of current developed from a given E. M. F. is 
determined. 

90. What is the meaning of the word quantity , when ap¬ 
plied to electricity i 

When applied to static electricity no clearer defini¬ 
tion can be given of the term quantity than the term 
itself ; and there is no reason why it should not have 
the same meaning when applied to electricity that it has 
when applied to any other force or substance, visible or 
invisible. 

The fact that we do not know that electricity has a 
separate existence, or is a distinct entity ; or that we do 
know that it is not an element, a fluid, or a substance, 
need not prevent us from speaking of its quantity, since 
we commonly speak of quantities of sound, light, and 
heat, without at all implying that a mass or volume 
of anything is actually present. When any body is 
charged with electricity it is very evident that the elec¬ 
tricity is there; that a certain well-defined amount is 
present, and that such an amount can be measured by 
an electrometer. When we, therefore, speak of such a 
quantity of electricity we simply mean the amount of 
electricity present. 

The word quantity, applied to current electricity, 
means literally the strength of the current, or the 
amount per second acting to produce heat, magnetism, 
chemical action, or any other of its effects. 

The strength of current must not be confounded with 
the strength of the battery which produces the current, 
but it may be termed the amount of electricity realized. 
It is the margin of effective electricity produced by any 


DEFINITIONS OF ELECTRICAL PROPERTIES, ETC. 93 

battery after the resistance of the circuit lias been over¬ 
come. 

All the most remarkable effects of the current, such 
as electrolysis, combustion of metals, the deflection of 
the galvanometer, and the production of magnetism and 
heat, are dependent on the quantity of electricity pass¬ 
ing. 

The quantity of electricity passing in a given circuit 
can be increased by increasing the electro-motive force, 
without proportionately increasing the resistance; or 
by diminishing the resistance. 

91. What are the standard units used in electrical measure¬ 
ments f 

A unit is the base of any system of measurement. 
Electricity has properties which it is frequently neces¬ 
sary to measure in order that its working value may be 
properly estimated. 

Now, that we may be able to state the results of such 
measurements, it is essential that we must have some 
standard terms which, when expressed, convey to the 
mind definite ideas, precisely as in measuring a distance 
we would say so many feet; or in expressing the capa¬ 
city of a tank, so many gallons ; or the contents of a 
solid block, so many cubic feet. 

Further, when one substance has several properties a 
different system of measurement is required for each 
property ; for as in a cubic block of wood we should 
measure one side of its surface by superficial measure, 
its contents by cubic measure, and its weight by still an¬ 
other system, and would state the result differently in 
each case, so the different electrical measurements each 

j 

have their own units, in which the results are ex¬ 
pressed. 

Designations have been given to the electrical units 
from the names of distinguished electricians and scien¬ 
tists. Thus the unit of electro-motive force is called 
the volt , from Volta; the unit of capacity is called the 
farad , from Faraday; the unit of resistance is called 


94 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

the ohm , from Ohm, the German physicist; while the 
units of current strength and of quantity, which have 
been of late years known respectively as the weber and 
weber per second , have been lately changed at the sug¬ 
gestion of the Electrical Congress held in Paris in 1882, 
the names ampere and coulomb having been substituted 
therefor. These latter names seem to meet with favor, 
and are certain to be universally adopted. 

92. What is the meaning of the term volt t 

The volt is the name of the practical unit of electro¬ 
motive force and of difference of potentials. Its pre¬ 
cise value is 0.9268 of a Daniell cell in good condition ; 
in other words, the Daniell cell is equal in E. M. F. 
to 1.079—one volt and seventy-nine thousandths. The 
Daniell cell may, therefore, for practical purposes be 
said to have an electro-motive force of one volt. 

The volt is equivalent to the electro-motive force re¬ 
quired to produce a current of the strength of one am¬ 
pere in a circuit having a total resistance of one ohm. 

An E. M. F. equal to one million volts is called a 
megavolt, and one-millionth of a volt is called a micro¬ 
volt. 

93. What is the standard unit of resistance , and how may it 
be defined t 

The unit which is almost universally used in this coun¬ 
try and in England is that fixed upon as a standard by 
a committee of the British Association. It is therefore 
sometimes called the B. A. unit, but more frequently the 
ohm , from Ohm, the distinguished German mathemati¬ 
cian, who first ascertained the laws of electrical resist¬ 
ance. It is a unit of resistance , in the same way that an 
inch is a unit of length or an ounce that of weight, and 
is approximately equal in resistance to a wire of pure 
copper one-twentieth of an inch in diameter and two 
hundred and fifty feet long, or of one-sixteentli of a 
mile of No. 9 galvanized-iron wire of the ordinary qual¬ 
ity. A microhm is a millionth of an ohm, and a meg¬ 
ohm is equal to a million ohms. 


DEFINITIONS OF ELECTRICAL PROPERTIES, ETC. 95 

94. IT hat is the unit of current strength , and how may it be 

defined f « 

There seems to have been heretofore considerable con¬ 
fusion regarding the name of this unit. Some years ago 
it was generally spoken of as a farad, tlie name now 
representing solely the unit of capacity. Later, and un¬ 
til the Electrical Congress of Paris in 1882, it has been 
called tlie loeber. At that Congress the name ampere 
was suggested, and may now be considered authorita¬ 
tive. 

It represents tlie strength of current passing in a cir¬ 
cuit having a total resistance of one ohm, with an E. M. 
F. of one volt. If the E. M. F. and the resistance both 
remain constant, the current strength will also be con¬ 
stant. 

Thus, if, speaking of a given circuit, we say that it has 
a current of fifty amperes, and we know that the resist¬ 
ance of the circuit is fifty ohms, we know at once that 
the' E. M. F. must be fifty volts. To calculate the 
strength of current we use Ohm’s law and divide the 
electro-motive force by the resistance. A milli-ampere 
is a thousandth part of an ampere, and is useful in com¬ 
puting magnitudes where the current strength is not 
great. The currents employed in telegraphy vary from 
four to two hundred and fifty milli-amperes, the latter 
being the approximate current strength fioAving in an 
ordinary local sounder circuit; currents utilized in elec¬ 
tric lighting vary between one and fifty amperes. 

95. What is the unit of quantity f 

This has until lately also been called a weber, but 
the name given by the Congress of Paris is “ coulomb .” 
The coulomb denotes the amount of electricity which a 
current of the strength of one ampere can furnish per 
second of time. 

In other words, it is the amount of electricity fur¬ 
nished in one second by an electro-motive force of one 
'rolt in a circuit having a total resistance of one ohm. 

It may also be defined as the amount of electricity 


96 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

which, with a difference of potential of one volt, will 
fully charge a condenser having a capacity of one 
farad. 

96. What is the unit of capacity , and how may it be defined t 

The farad is the unit of capacity , and is as necessary 

as a unit of resistance or electro-motive force. It is 
used in determining the amount of charge a condenser 
is capable of. A condenser or Leyden jar of the capa¬ 
city of one farad is one which is fully charged by the 
amount of electricity which, with an electro-motive force 
of one volt, would How through a resistance of one ohm 
in one second of time. 

It may also be defined by saying that it represents the 
capacity of a condenser which contains one coulomb of 
electricity when the difference of potential between its 
opposing plates is one volt. A microfarad is a millionth 
of a farad, and a megafarad is one million farads. 

In actual practice the farad is much too large a quan¬ 
tity, and the unit adopted is the microfarad. 

97. What is Ohm's laic f 

It is one of the most important of the laws which gov¬ 
ern the transmission and distribution of electricity, and 
•was promulgated by Dr. G. S. Ohm, of Nuremberg, Ger¬ 
many, as early as 1827. Stated as concisely and plainly 
as possible, it is as follows : 

The effective strength of current in any given circuit 
is equal to the electro-motiveforce divided by the total 
resistance / and it is the basis of all electrical measure¬ 
ments. 

It may also be represented as below: In any circuit 
the strength of current is equal to the E. M. F. divided 
by the resistance; therefore the resistance equals the 
electro-motive force divided by the current, and the 
electro-motive force equals the current multiplied by 
the resistance. 

It is obvious, then, from the above considerations that, 
knowing two of these magnitudes, we can readily calcu¬ 
late the third. 


7 


DEFINITIONS OF ELECTRICAL PROPERTIES, ETC. 97 

To obtain definite results we must use definite units ; 
for example, we will suppose a battery of 100 cells, and 
call each cell an E. M. F. of one volt, which will give us 
a total E. M. F. of 100 volts. We will further suppose 
a resistance in the battery itself of 20 ohms, and in the 
line and instrument of 30 ohms, making a total resist¬ 
ance of 50 ohms. Now, as the E. M. F. divided by the 
resistance gives the current, all we have to do is to di¬ 
vide the 100 by 50, and we have a quotient of 2—show¬ 
ing that with an E M. F. of 100 volts, and a resistance 
of 50 ohms, the strength of current flowing in the cir¬ 
cuit is equal to two webers, or amperes. 

It follows, then, that if the electro-motive force is In¬ 
creased, while the resistance is maintained the same, the 
strength of current is also proportionately increased; 
and that if the resistance of the circuit is increased, 
while the E. M. F. is left unaltered, the current is pro¬ 
portionately decreased. 


CHAPTER IX, 


ELECTRICAL MEASUREMENTS. 

98. What is a galvanometer i 

A galvanometer is an instrument for detecting, indi¬ 
cating, or measuring currents of electricity. 

When used only for detecting or indicating such cur¬ 
rents the instrument is more properly called a galvano- 
scope. Galvanometers are made in many forms and 

are used in several different ways, but 
are all based on the fundamental fact 
that a magnetic needle is deflected 
from its natural position by the 
passage of a current of electricity 
in a conductor placed parallel to it. 
When the conductor is carried over 
the needle and back on the other 
side, as in Figure 42, the effect is 
doubled; and, of course, if we repeat 
the operation a great many times, using insulated wire, 
thus forming a coil in which the needle is freely sus¬ 
pended, the effect may be multiplied almost indefi¬ 
nitely. 

All galvanometers, then, consist of a coil of insulated 
wire and a magnetic needle delicately suspended, so 
as to be easily deflected by the passage of a current 
through the coil. These, in conjunction with a dial- 
plate, graduated so that we may intelligently interpret 
the movements of the needle, are the only essential 
features of the instrument. 

Horizontal galvanometers are more sensitive than ver¬ 
tical ones and are in more general use, a very good form 
for use in connection with a Wheatstone bridge being 
shown in Figure 43. In using a galvanometer-for any 

98 






















ELECTRICAL MEASUREMENTS. 


99 


purpose an instrument of low resistance is the fittest 
one to use for testing low resistances ; and tlie greater 
the resistance to be tested the finer should be the wire, 



Fig. 43. 


the greater the number of convolutions, and, conse¬ 
quently, the higher the resistance of the galvanometer. 

99. When and by whom was the galvanometer invented t 

The galvanometer is one of the earliest results of Oer¬ 
sted’s discovery. It was, in fact, in the same year (1820) 
that the first galvanometer was invented by Professor 
Johann S. C. Schweigger, of Halle, who passed a num¬ 
ber of turns of insulated wire round the compass needle, 
thus multiplying the galvanic effect and constructing a 
galvanometer. An instrument of different form was 
soon afterward independently devised by Johann C. 
Poggendorff, of Berlin ; and, as a description of this 
latter was published prior to that of Schweigger, Pog¬ 
gendorff has been thought by some to be the original 
inventor. 

The invention of the galvanometer is the basis of the 
needle system of telegraphy. 

100. What are the principal galvanometers now in use ? 

The tangent and sine galvanometers, the differential, 

Thomson’s reflecting galvanometer, and those con* 























100 ELECTRICITY, MAGNETISM, AND TELEGRAPHY'. 

structed on tlie Wheatstone bridge principle, which lat¬ 
ter usually comprise also the necessary resistance-coils. 

101. What are the principal uses of a galvanometer % 

Besides the use implied by the name— i. e ., that of de¬ 
tecting and measuring galvanic currents—the galvano¬ 
meter is invaluable in practical telegraphy, and is em¬ 
ployed in the testing and measurement of instruments 
and circuits for conductivity resistance ; and the latter 
also for insulation resistance. It is also used in the 
localization of faults on telegraph lines and in cables ; 
in the measurement of internal resistance, and estima¬ 
tion of the electro-motive force of batteries ; and, in the 
case of long submarine lines, as a receiving instrument 
for telegraphic signals. 

102. What is an astatic galvanometer f 

It is a peculiar arrangement suggested by Professor 
Cummings in order to increase the sensibility of the 
galvanometer. Two needles are freely suspended on 
the same axis, parallel to each other, but with their 
poles placed in contrary directions—the north pole of 
the upper being directly over the south pole of the 

lower. The sensibility of the galvano- 
meter is increased, because the direc¬ 
tive force of the earth is neutralized, 
since the two needles are opposed to 
each other. If the needles could be 
made exactly equal to each other in 
magnetic power they would stand in¬ 
differently in any position in which 
they were placed ; but in practice one 
needle is always a little stronger than the other, and 
the pair will, therefore, settle in a north and south direc¬ 
tion. Each needle may have its own coil, the coils 
being joined so that the current circulates in opposite 
directions around the two and deflects both needles simi¬ 
larly. On the same axis with the’needles, Tbut above the 
graduated circle, is a pointer to denote the deflections. 
The nearer the two needles are to each other in magnetic 
























ELECTRICAL MEASUREMENTS. 


101 


strength, the slower will be the vibrations of the pair 
and the greater the delicacy of the galvanometer. 

Two needles so mounted and arranged in coils consti¬ 
tute an astatic galvanometer. 

103. What is a tangent galvanometer , and how is it used f 

It is an instrument invented by M. Pouillet, a French 
electrician. Its principle is that the strength of cur- 
rent , as measured hy the tangent galvanometer , is pro¬ 
portional to the tangent of the angle of deflection of the 
needle . It is thought by many electricians to be the 
most useful and convenient form of galvanometer for 
general purposes. It consists essentially of coils of 
wire wound in a deep groove in the circumference of 
a brass ring about six inches in diameter, with a small 
magnetized needle hung at its centre and moving over 
a graduated circle. The length of the needle must be 
small compared with the diameter of the coil, in order 
that the influence of the coil may, as far as possible, be 
the same whatever the angle of deflection of the needle. 

A form of this instrument is made in the United 
States with the above object specially in view. It 
was devised by Dr. Bradley, of Jersey City, and is de¬ 
scribed as follows : ‘ ‘ The needle is composed of several 
parallel strips of steel, mounted on a ring of aluminum, 
and trimmed to form a circle. By this means all parts 
of the needle are subjected to the influence of the coil 
throughout the entire deflection. Four coils are used, 
the first about 150 ohms resistance, the second 25 to 30 
ohms, the third one or two ohms, and the fourth is a 
strip of sheet copper or brass, which is wound two or 
three times around the needle.” 

The first coil is used for high resistances, the last for 
very low resistances, and the other two for medium re¬ 
sistances. 

It will do no harm to state here, for the benefit of the 
student who is no mathematician, that a tangent is a 
straight line which touches at any one point the circum¬ 
ference of a given circle. 


102 ELECTRICITY, MAGNETISM, AND TELEGRAPH!. 

In the case of the tangent galvanometer the dial of 
the instrument is the given circle, and the point at 
which the tangent touches the circle must be the zero- 

point. 

The tangent is, therefore, an imaginary line, which 
must be parallel to the diameter that connects the de¬ 
gree of ninety on one side to the same degree on the* 
other side, and at right angles to the diameter, 01 line- 
connecting the two zero-points. Now, if the needle is* 
deflected by a given current to twenty degrees, a current 
of double the strength will not deflect the needle a sec¬ 
ond twenty degrees, but to double the distance measured 
off on the tangent line. 

This instrument is very useful in testing overhead 
lines, or measuring resistances by substitution of a 
known for an unknown resistance. It is much used 
in England as an instrument for making periodical line 
tests, and is employed for almost every general purpose 
in this country. A modification of the tangent galvano¬ 
meter was constructed by Mr. Gaugain by suspending 
the magnet eccentrically at a point in the axis of the 
coil distant from the centre by half the radius of the 
coil. It is, however, proved by Clerk Maxwell that 
this modification is in reality the reverse of an improve¬ 
ment. The instrument was really improved by Helm¬ 
holtz, who placed two equal, parallel, and vertical coils, 
one on each side of the needle, each at a distance from 
it equal to half the common radius. The proper deflec¬ 
tion to work with is from thirty to fifty degrees. If a 
less deflection is used a small error in reading off makes 
a large one when worked out; and if a larger deflection 
than fifty degrees is used a large alteration in resist¬ 
ance will produce but little effect on a galvanometer. 

Care must be taken, using this instrument, to have 
the scale in proper position, so that the^ends of the 
pointer stand over the zero-points. If the deflection 
be too low when testing, try one of the other coils un¬ 
til a proper deflection is found, always taking care to 


ELECTRICAL MEASUREMENTS. 


103 


use the coil which most nearly approximates the resist¬ 
ance to be measured. 

If one coil gives too high a deflection and the next 
one too low, vary the battery power. This instrument 
is generally used with a table of tangents, so that when 
the needle is deflected to any degree, and the result is 
read off, the tangent of that degree may be ascertained 
by reference to the table. 

The Western Union Telegraph Company uses a very 
good tangent galvanometer, which is shown in Figure 
45. 



Fig. 45. 


This instrument is mounted on a circular hard-rubber 
base, 7| inches diameter, provided with levelling-screws 
and anchoring-points. The galvanometer consists of a 
magnetized needle -J inch in length, suspended at the 
centre of a ring, 6 inches in diameter, containing the 
coils. The coils are live in number, of the resistances 
0, 1, 10, 50, and 150 ohms. The flrst is a stout copper 






































104 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

band of inappreciable resistance ; tlie others are of dif¬ 
ferent-sized copper wires carefully insulated. Five ter¬ 
minals are provided, tlie plug-holes of which are marked 
respectively 0, 1, 10, 50, and 150. The ends of the coils 
are so arranged that the plug inserted at the terminal 
marked 150 puts in circuit all the coils ; at the terminal 
marked 50, all except the 150-ohm coil; and so on, till 
at the zero terminal only the copper band is in circuit. 

Fixed to the needle, which is balanced on jewel and 
point, is an aluminum pointer at right angles, extending 
across a live-inch dial immediately beneath. On one side 
the dial is divided into degrees ; on the other it is gradu¬ 
ated, the figures of the scale corresponding to the tan¬ 
gent of the angles of deflection. 

This galvanometer is made by J. H. Bunnell & Co., of 
New York, from whose pamphlet we quote the foregoing 
description. 

104. What is a sine galvanometer, and lioiv is if used? 

A sine galvanometer is one in which the coils are 
made movable, so as to be capable of revolving on the 
axis around which the needle turns. A scale graduated 
with degrees is attached to the coil, so that the angle 
through which it is turned can be observed. When the 
needle is deflected by a current passing through the 
coil, the coils are turned by hand, following tlie needle 
in its deflection; as the coils are turned the needle di¬ 
verges still more, but the angle it makes with the coils 
becomes less and less, until at length a point is attained 
at which'the needle remains parallel with the coil. 

When this point is reached the influence of the earth’s 
magnetism exactly balances the deflective force of the 
current. 

The strength of the current that produces the deflec¬ 
tion will then be directly proportional to the sine of the 
angle through which the coil is turned. 

The sine of any number of degrees is that" part of the 
diameter of a circle which is included between a line 
drawn from its centre to the zero-point of the gradua- 


ELECTRICAL MEASUREMENTS. 


105 


tion circle, and another line, parallel to the first, cutting 
the circle at the degree whose sine is required. If a cur¬ 
rent of known strength, then, deflects the needle to an 
angle of thirty degrees, and the current to be compared 
deflects the needle to an angle of forty-five degrees, the 
strength of the second current is to the first as the sine 
of forty-five degrees is to the sine of thirty degrees. 
The usual practice is to read off the degree and refer to 
a table of sines for the required sine. In using the sine 
galvanometer it is necessary to be careful that, if the 
needle is at zero at starting, it is brought back exactly 
to zero again. It is a very accurate instrument, if prop¬ 
erly managed, and is used chiefly for measuring and • 
comparing weak currents. 

105. What is a differential galvanometer , and how is it used f 

It is an instrument invented by M. Becquerel. The 
needle is poised or suspended like that of the sine and 
tangent galvanometers, but is surrounded by a coil com¬ 
posed of two wires of equal length, size, and conduc¬ 
tivity. 

The ends of these coils are so connected that a current 
made to traverse them passes through the two coils in 
opposite directions, and therefore, when the current in 
each coil is equal, the effect of one coil is completely 
neutralized by that of the other, and the needle is not 
deflected. If now one current be made stronger than 
the other the balance will be destroyed and the needle 
will be moved by the stronger current. 

This instrument is used to measure resistances by 
comparing them with standard resistance-coils. The re¬ 
sistance to be measured is inserted in the circuit with 
one of the galvanometer coil-wires, and the standard 
resistance in circuit with the other coil-wire. The 
standard resistance is usually inserted by drawing out 
plugs, or, as it is technically called, “unplugging resist¬ 
ance.” We will suppose that a telegraph line is to be 
measured for conductivity resistance: it is placed in 
circuit with one of the galvanometer-coils, with the 


106 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

effect, of course, of greatly increasing tlie resistance on 
that side; and, in consequence, a large proportion of 
the current returns through the other side, where as^ 
yet there is only the resistance of the galvanometer- 
coil, the needle being strongly deflected. We then un¬ 
plug resistance from the rheostat on the opposite side to 
that of the resistance to be measured, until the needle is 
balanced; and the amount thus unplugged equals tine 
resistance to be measured. 

In order that widely differing resistances may be bal¬ 
anced, one coil is provided with shunts. These, when 
used, vary the sensibility of the galvanometer, and, by 
diverting a portion of the current, permit a small resist¬ 
ance on one side to balance a large resistance on the 
other. For example, if we have a resistance to be mea¬ 
sured, and the comparison-coils at hand are not large 
enough to be substituted for the unknown resistance 
without the use of a shunt, we employ a shunt of, say, 
one-ninety-ninth of the resistance of the galvanometer- 
coil. The current passing through that coil will then 
be one-hundredth of the original current, because the 
ninety-nine hundredths pass through the lesser resist¬ 
ance of the shunt. Now, as the current passing through 
the coil is but one-hundredth part of the entire current 
which, if unshunted, would pass through it, it follows 
that the resistance which must be unplugged to balance 
the unknown resistance will actually be but one-liun- 
dredtli part of the resistance required. 

After using the shunt of one-ninety-ninth, then, we 
will suppose that, to balance the needle, we have to- 
unplug five hundred ohms, which is, as stated above, 
just one-hundredth part of the true unknown resis¬ 
tance. 

All we then have to do is to multiply the five hundred 
by one hundred, and the result is equal to the unknown 
resistance—that is, fifty thousand ohms. 

It is particularly important that eacli coil should be- 
perfectly insulated from the other, as imperfect insula- 


ELECTRICAL MEASUREMENTS. 107 

tion is tlie worst defect a galvanometer of this class can 
have. 

106. Describe Thomson's reflecting galvanometer. 

Thomson’s reflecting galvanometer is the most sensi¬ 
tive instrument in use, and is almost invariably em¬ 
ployed when very high resistances have to be mea¬ 
sured, and also when great accuracy is required. Its 
principle is that of delicately suspending a very light 
and small magnetic needle within a coil consisting of 
the greatest possible number of turns of wire, and of 
magnifying the movements of the needle so surrounded 
by a beam of light, reflected from a small mirror fixed 
to the needle, on a graduated scale about three feet 
away. 

Figure 46 shows the instrument in side elevation, 
including the lamp and graduated scale, the galvano¬ 
meter being in section. 

Figure 47 is a cross-section through the coils, show¬ 
ing the needle. 

As usually made it has two circular coils, R, sepa¬ 
rated from one another by a brass frame, B, in which 
the needle, A, is suspended ; the coils completely sur¬ 
round the needle, so that, no matter wliat angles they 
are deflected to, they are always under the influence of 
the coils. The instrument is generally made astatic, 
and the two needles are connected one with the other 
by an aluminum wire. Its base is usually made of 
ebonite, and is provided with spirit-levels at right 
angles to each other, so that the whole instrument can 
be set accurately level by means of levelling screws. 

Although the coils are in a brass case, they are wound 
on bobbins of non-conducting material. The magnetic 
needles are very small, usually not more than three 
eighths of an inch long, and to the one in the upper¬ 
most coil, if an astatic combination is used, is fixed 
a very small mirror, a. The needle and the mirror 
are suspended by a silk fibre from an adjustable 
screw, b. 


108 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


The beam of light before mentioned is thrown from a 
lamp, E, placed behind a screen, Y, and falls on the 
needle-mirror, which is slightly inclined so as to reflect 
on a graduated scale, I, fixed on a stand, F, the said 
scale being placed immediately above the point where 
the beam leaves the lamp. 

The scale is a straight and flat surface, and is gene¬ 
rally marked with three hundred and sixty divisions 
on each side of the zero-point. 

The galvanometer-coils are insulated from the frame 
by a disc of hard rubber, T. 

In the best forms of instrument a glass shade is 
placed over the coils, and from the centre of its top a 
brass rod rises. A short brass tube slides on the rod 
and carries a weak bar magnet, slightly curved, which 
is fixed at right angles to the rod. This magnet can be 
slid up or down, or twisted around, and the sensitiveness 
of the needle thereby increased or diminished. By 
turning the bar magnet so that its north pole points to 
the north, it will act on the needle with a magnetism 
opposing that of the earth, and tend to turn the needles 
around. By sliding the bar gradually down a point is 
reached where the earth’s magnetism is just counter¬ 
acted. When this point is arrived at the needle will 
stand at any position. The regulating magnet is then 
raised about an inch higher than the neutralizing posi¬ 
tion, when the earth’s magnetism will be just sufficient 
to keep the needles north and south. They are, there¬ 
fore, very sensitive to any external force, and move 
when a very weak current passes through the coils. 

In using this instrument no iron must be near it, and 
the testing operator should remove any keys or knives 
from his person, as so sensitive an instrument is often 
affected by such bodies. 

These instruments, when intended to measure large 
resistances, are often wound with German-silver wire, 
and their own resistance is sometimes as high as fifty 
thousand ohms. 


ELECTRICAL MEASUREMENTS. 


109 


Such an instrument will give, with one cell of Daniell’s 
battery, a deflection of two hundred divisions when 
measuring an outside resistance of ten million ohms. 


9 

tp 


op 



The reflecting galvanometer, besides being used for 
delicate measurements and high resistances, is much 

























































































110 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

employed as a receiving instrument for telegraphic sig¬ 
nals sent through long submarine cables. A modifica¬ 
tion, known as Thomson's marine galvanometer, is used 
on ships laying cables, as a testing instrument, and for 
similar purposes. It is so arranged as not to be affected 
by the oscillations of the vessel, the fibre carrying the 
needle being attached to both top and bottom of the 
frame in which it is suspended. 

107. What is the Wheatstone bridge ? 

The Wheatstone bridge, though usually classed with 
galvanometers, and explained under that head by most 
of the text-books on electricity, is, strictly speaking, 
not a galvanometer, but a system of measurement, or 
an arrangement of circuits whereby a galvanometer can 
be most advantageously employed. It was devised by 
Mr. S. Hunter Christie, and described by him in the 
Philosophical Magazine in 1836. But it was not much 
noticed or used until introduced by Wheatstone in 
1843, in a paper forwarded to the Royal Society de¬ 
scribing several new instruments for electrical measure¬ 
ments. Although previously described by Christie, it 
is almost universally known as Wheatstone's bridge or 
balance. It is usually represented as in Figure 48, by 
a diagram with the wires arranged in the form of a 
lozenge. 

The lozenge is composed of four wires, which, for con¬ 
venience, we will call A, B, C, and D. Two of the 

opposite corners of 
the lozenge are con¬ 
nected by a wire 
2 with a galvanome¬ 
ter in circuit, and 
the other two oppo¬ 
site corners are re¬ 
spectively connect¬ 
ed to the two poles 
rig- 48. of a battery. The 

two wires which converge to a point at the left hand we 









ELECTRICAL MEASUREMENTS. 


Ill 


will call A and C, and the two that converge to the 
right hand we will call B and D. 

Adjustable resistances are inserted in the branches 
A and C, a comparison coil, or rheostat, in one of the 
"branches B D, and the resistance to be measured in the 
other. 

When all of the resistances are equal and the battery 
circuit is closed the galvanometer on the cross-wire 
will not be affected ; because, as electrical currents are 
caused by a difference of potential, and the two points 
connected by the galvanometer are, under those circum¬ 
stances, at the same potential, it is obvious that no cur¬ 
rent will pass through the cross-wire and galvanometer, 
there being no force tending to cause a current therein. 

Again, when branch A bears the same proportion to 
C that B does to D, no current will pass on the cross¬ 
wire, because the battery current having divided at the 
point of divergence of the wires A and C, in inverse 
proportion to the several resistances of those branches, 
that proportion of the current which is in each branch, 
on arriving at the crossing-point of the bridge, will still 
be at the same potential. 

But if the resistance A does not bear the same pro¬ 
portion to C that B does to D, the needle will be 
strongly deflected. Hence it will be readily seen that 
unknown resistances can be accurately measured by 
inserting them, for example, into the branch D, and 
varying the other resistances—chiefly that in the branch 
B—until the needle stands at zero. The proper propor¬ 
tion is now restored, and the unknown resistance is 
ascertained by a simple calculation in proportion, or the 
rule of three. For instance, we will suppose that in A 
we have a resistance of 100 ohms, in C 10 ohms. We 
then insert our unknown resistance in D, and a rheo¬ 
stat or resistance-box in B. When we close the battery 
circuit the needle deflects. We then vary the resistance 
in the box until the needle remains at zero. To ob¬ 
tain this result we have unplugged 200 ohms. There 


112 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

fore, as 100 is to 10, so is 200 to 20—the resistance re¬ 
quired. 

This is merely given as an illustration of the system. 
In practice, to measure a resistance within the range of 
the rheostat, tlie resistances in the branches A and C 
are made equal, because when they are equal the gal¬ 
vanometer is most sensitive. But, as it will readily be 
seen from the foregoing example, resistances both of ex¬ 
tremely great and extremely small magnitudes can be 
measured by this system. 

The bridge apparatus generally embraces a rheostat 
and galvanometer with two keys, one to make and 
break the battery circuit, the other to make and break 
tlie bridge wire. The rheostat usually is made with the 
resistances of the three arms A, C, and B all in one 
box, and with the branches A and C each consisting of 
three coils—10,100, and 1,000 ohms respectively—any of 
which may be used by tlie withdrawal of its short-cir¬ 
cuiting plug. The arm B is a set of resistance-coils vary¬ 
ing from 1 to 4,000 or 5,000 olims, while the arm D is 
provided with two binding-screws for the reception of 
the resistance to be measured. Circuits which only 
have one end within reach can be measured by putting 
one pole of the battery to earth, the branch B also to 
earth, and extending the branch D to the circuit to be 
measured, which must also be grounded at the distant 
end. In using this apparatus, when the resistance to 
be measured is approximately known, the proper plugs 
must be first taken out of A and C; the battery key 
should first be pressed, then the galvanometer key, 
making very short contacts with the latter, until the 
needle is nearly balanced. When the balance is ob¬ 
tained it should be ascertained whether or not the 
needle will remain steady when the contact is made 
and broken. 

Almost any good galvanometer can be used with the 
bridge system of measurement. The bridge is not now 
exclusively used for measurements, but has been utilized 


ELECTRICAL MEASUREMENTS, 


113 


also in duplex telegraphy and in the construction of 
sensitive burglar-alarm telegraphs. 

108. TT hat is meant by the constant of a galvanometer f 

The constant ol‘ a galvanometer means simply the de¬ 
flection of the galvanometer-needle, obtained through a 
standard resistance by a standard battery. The ex- 
pression is used more frequently in England than in 
America ; and there, as explained by Kempe, the term 
constant is applied to “the product of the deflection 
in degrees, and the resistance in ohms, when multiplied 
together. For example : With a battery, a galvanome¬ 
ter, and a resistance of 1,000 ohms in circuit, a deflec¬ 
tion of 20 degrees is obtained. The 1,000 is then multi- 
plied by the 20, and the product, 20,000, is called the 
constant.” 

If wires are to be tested the constant is first taken, as 
above, after which the wires are inserted in circuit, one 
by one. To obtain the results in ohms the constant is 
divided by the deflection obtained from each. 

109. What is a rheostat f To ivhat apparatus is the name 
now applied i How is it used t 

The name rheostat was originally given by Wheat¬ 
stone to an instrument devised by himself for the pur¬ 
pose of varying at will the amount of resistance in a cir¬ 
cuit. 

Two cylinders, one of metal and the other of some 
non-conducting material, were arranged near each other, 
so that a fine German-silver wire could be rolled and un¬ 
rolled from one to the other, the resistance of the wire 
being known. When the fine wire was all rolled on the 
metal cylinder it had no appreciable resistance, as the 
current would travel through the mass of the roller ; 
but when the wire was wound on the wooden or rub¬ 
ber cylinder in grooves prepared for it, the current was 
forced to pass through the entire length of the wire un¬ 
rolled. By this means resistance was added to or taken 
from the circuit. This apparatus is now scarcely ever 
used, but the name survives, and at the present day 


114 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

when we speak of a rheostat we mean a set of standard 
resistance-coils arranged together in a box and used for 
electrical measurements. Such an apparatus is show 
in Figure 49. 



Fig. 49. 


Coils of wire, varying in resistance—for instance, from 
T V of an ohm to 5,000 ohms—are arranged in a box, 
their terminal wires being permanently connected to¬ 
gether by a series of stout brass plates on the ebonite 
cover of the box. Conical brass plugs, inserted between 
the brass plates, serve to throw the coils in and out of 
circuit. 

When all the plugs are in, and the resistance-box is 
in circuit, the current takes the short path through the 
brass plates and the plugs ; but when any plug is with¬ 
drawn the short route between the two brass plates 
which that particular plug connected is broken, and the 
current is consequently forced through the coil below, 
and the resistance of that coil is added to the circuit. It 
will thus be seen that, by varying the arrangement of 
the plugs, the resistance may also be varied almost in¬ 
definitely. In making a box of resistance-coils thick 
wire should be used for the small resistances, for two 












































































































































































ELECTRICAL MEASUREMENTS. 


115 


reasons : first, they are easier to adjust; and, secondly, 
they are less likely to become deranged by powerful cur¬ 
rents. 

Pile wire used must be of some metal which is not 
easily affected by changes of temperature. German 
silver is generally used. 

The wire is insulated by two coatings of silk, and is 
wound double so as to eliminate self-induction, and 
also that it may not affect galvanometers in its vicin¬ 
ity. When coiled the bobbins are soaked in melted 
paraffine, which maintains their insulation. The high 
resistances are made of fine wire, in order to economize 
space. 

The following precautions are necessary in using re¬ 
sistance-coils : Keep the brass plugs clean and bright ; 
because, if dirty, they will not entirely cut out the 
coils. When a plug is inserted do not simply push 
it in the hole, but give it a twist, and thereby insure 
good contact. Before commencing to use a rheostat- 
give all the plugs a twist, to be sure that none of them 
are loose ; and, finally, touch the brass plugs as little as 
possible with the fingers. 

110. Give some simple methods of measuring resistance. 

The earliest method of measuring resistances was by 
using a common galvanometer multiplier, or a sine or 
tangent galvanometer, to place the resistance to be mea¬ 
sured in circuit alternately with a standard resistance. 
If the deflection remained the same in both cases, it 
was assumed that the resistances were equal. The diffi¬ 
culty in this method was that the electro-motive force 
and internal resistance of the battery were supposed to 
remain constant—a condition which they rarely fulfil. 
The desire of obviating this difficulty was the cause of 
the introduction of the differential galvanometer and 
Wheatstone bridge, in both of which instruments the 
result is.attained irrespective of battery variation. The 
differential method was much used by Becquerel and 
others at one time, but it is entirely superseded in Eng- 


116 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

land by the bridge method. In the United States the 
method that happens to be most convenient at the 
time is generally used. As the rheostat is now often 
made with a switch that can be instantly moved from 
the standard resistance to the resistance which is to be 
measured, the objection to the substitution method is 
substantially removed. 

To measure resistance by any ordinary galvanometer, 
using resistance-coils, we must first connect up the gal¬ 
vanometer in circuit with the resistance to be measured 
and a battery sufficient to produce a good deflection. 
Note the deflection produced, then substitute the rheo¬ 
stat for the unknown resistance, and unplug resistance 
until the needle shows the same deflection as before. 
Add the figures on the holes unplugged, and we have 
the required resistance. If we use the rheostat provid¬ 
ed with the switch, all we have to do is to throw over 
the switch, and we can verify the result by moving the 
switch quickly a number of times. If the needle stands 
still at the same deflection, whichever side the switch 
rests, the result is correct. In using a differential gal¬ 
vanometer we connect the rheostat on one side and the 
unknown resistance on the other, and vary the resist- 
ance in the rheostat until the needle stands at zero. 
The resistance unplugged equals the resistance required. 

In using the Wheatstone bridge system the unknown 
resistance is inserted in the side of the bridge, opposite 
to the variable resistance. If we have any idea what the 
resistance to be .measured should be, we first unplug 
equal resistances on the first two sides of the bridge, 
each as near to the unknown resistance as may be. We 
then unplug resistance on the third side until the needle 
remains at zero when the battery key is pressed down. 
The resistance unplugged from the comparison-coils 
then equals the resistance required. For example : We 
have a bridge system, the first and second branches of 
which each possess resistance-coils of 10, 100, and 1,000 
ohms, any or all of which may be unplugged at will 


ELECTRICAL MEASUREMENTS. 


117 


the third branch lias a series of coils, from 1 to 4,000 
ohms, and the fourth has binding-posts for the in¬ 
sertion of the resistance to be measured. This resist¬ 
ance we suppose to be about 400 ohms. The 100-ohm 
coils in branches one and two being the nearest fig¬ 
ures to the supposed resistance, we unplug them, and, 
pressing the battery key, find that the needle violently 
deflects. We then unplug 400 ohms on branch three, 
and again press the battery key, when we find that the 
needle still deflects slightly. We unplug 50 ohms more, 
and find the needle has now passed the zero-point and 
deflects to the opposite side, showing that we have un¬ 
plugged too much. We replace the 50-olim plug and 
draw 20. The needle will now, perhaps, stand at zero 
when the key is pressed, showing that the resistance re¬ 
quired is 420 ohms. The reason for withdrawing the 
100-ohm coils on the first and second branches is that the 
galvanometer is most sensitive when all the branches are 
equal. It is, therefore, as sensitive as possible when the 
branches are as nearly equal as possible. 

When we measure the resistance of a wire the dis¬ 
tant end of which is to earth, we join the near end of the 
wire to the terminal of branch four, put one end of the 
battery to earth, and also put the terminal of branch 
three to earth, and proceed as before. 

111. How may three parallel line-wires he measured without 
using an earth-wire % 

Call the wires 1, 2, and 3. The resistance of each is 
required ; 1 and 2 are connected at the distant end, and 
the loop measured, the result being, we will say, 300 
ohms. We then connect 1 and 3 at the distant end, and, 
measuring, find the result to be 600 ohms. Lastly, we 
loop 2 and 3, and, measuring again, find the resistance 
to be 700 ohms. To get the resistance of No. 1 we add 
the first two results together—the 300 and the 600 ohms 
—the sum being 900, which is obviously the sum of the 
resistances of all the wires ; the first being doubled, as 
it was measured twice. We then subtract the third 


11S ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

result from the sum so obtained, deducting 700—the 
amount of resistance of Nos 2 and 3—from 900, and find 
the remainder to be 200. This divided by 2, because 
No. 1 was twice measured, gives us 100 ohms as the re¬ 
sistance of No. 1. The resistance of No. 2 is ascertained 
similarly—that is, by adding the first and third results, 
subtracting the second, and dividing by 2, and is then 
found to be 200 ohms. The resistance of No. 3 is ascer¬ 
tained by adding the second and third results, subtract¬ 
ing the first from the sum, and dividing by 2, leaving 
the final result 500 ohms. That these final results are 
correct may, of course, be readily proved by adding 
them together. 

112. What is meant by the internal resistance of a battery f 

It must not be forgotten that the battery is a part of 
the circuit, and must therefore be considered not merely 
as a producer but also as a conductor of the current. 
Considering it in this light, it is obvious that it must of 
necessity bear its proportion of the resistance of the cir¬ 
cuit, since, as previously stated, all substances present 
more or less resistance to the passage of electricity. The 
internal resistance of a battery consists, first, of the re¬ 
sistance of the liquids, and, secondly, of the porous cell, 
if one is used, to separate the liquids. 

It is modified by the size of the plates, for the larger 
the plates are, the greater the area of the liquid, and 
consequently the less its resistance ; by their distance 
from eacli other, for the nearer they are placed the 
shorter is the liquid conductor ; and by the nature of 
the liquid in which they are immersed, for acid solutions 
usually offer much less resistance than saline liquids. 

Both acid and saline solutions, though the best of 
liquid non-metallic conductors, offer enormously more 
resistance than metals, as will be seen from the follow¬ 
ing comparison : 

If the resistance of copper be taken as 1, mercury may 
be taken as 50, a solution of water twelve parts and sul¬ 
phuric acid one part will be 1,500,000, a solution satu- 


119 


EL EOTRIC A L M E AS U REM ENTS. 

rated with zinc sulphate 16,000,000, and a saturated 
solution of copper sulphate 17,000,000. 

r lhe resistance of a battery increases in direct propor¬ 
tion to the number of cells which compose it—that is, if 
one cell have an internal resistance of 1 ohm, a battery 
of 10 similar cells will have a resistance of 10 ohms. 

If the two poles of a battery are connected by the 
shortest and thickest wire practicable, the internal resist¬ 
ance of the battery constitutes, practically, the entire 
resistance of the circuit. 

The voltaic battery is, therefore, a type of all force- 
producing machines, in that it produces force and at 
the same time offers a resistance to that force; as, for 
instance, in a steam-engine the friction of the steam in 
the pipes, of the piston in the cylinder, and of the shafts 
in the bearings cannot be avoided. 

The internal resistance of some of the cells in common 
use is given below : 

Grove, half an ohm ; Daniell, 3 to 5 ohms ; gravity, 
2 to 4 ohms ; Leclanche, about 1 ohm ; Minot to, 10 to 
20 ohms. 

113 . Describe the simplest and best methods of measuring the 
interned resistance of a battery. 

There are various methods of determining the internal 
resistance of a battery. We give three ways which are 
as simple as any. The first, often called Mance’s me¬ 
thod, from its discoverer, is to place the battery to be 
measured in the fourth branch of a Wheatstone bridge. 
Let the first two branches be fixed resistances, and the 
third a rheostat or adjustable resistance. The galva¬ 
nometer is kept in the usual place on the cross-wire, but 
in the usual place of the battery we substitute a key, 
which permits us to connect or disconnect the wires, 
thereby enabling us to close or open the circuit at the 
point where the battery is generally placed. The adjus¬ 
table resistance is then varied until the making and 
breaking of contact by the key does not alter the de¬ 
flection of the needle. Then, as the resistance in branch. 


120 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

1 of the bridge is to branch 2, so is the resistance un¬ 
plugged from the rheostat in branch 3 to the internal 
resistance of the battery in branch 4; or, if the two 
branches at the first end are made equal, the resistance 
of the battery is also equal to that of the rheostat. 

To illustrate : We will call the four branches of the 
bridge A, 13, C, and D, and have a resistance of 10 ohms 
in each of the branches A and B. We place the battery 
to be measured in D, and the rheostat in C. We then 
close the key and the needle deflects ; but on raising 
the key the deflection alters materially. We unplug, 
say, 50 ohms from the rheostat, and find then that the 
deflection remains the same, whether we depress or raise 
the key. Then, as A and B are equal, both being 10 
ohms, 33 must also be equal to C—that is, 50 ohms. 
This method is practically independent of the galva¬ 
nometer resistance, and is extremely accurate, because 
it is not affected by variations in the strength of the 
battery. 

As in measuring the resistance of a galvanometer by 
its own deflection, it will generally be necessary to adopt 
some method of reducing the deflection, in order to ob¬ 
tain an accurate measurement. This may sometimes, 
when the instrument is not very sensitive, be done by 
making the branch resistances unequal. v The desired 
end may be gained more effectually by shunting the 
galvanometer. 

In the second method the tangent or sine galvano¬ 
meter may be used. Connect a rheostat, a tangent 
galvanometer, and the battery to be measured in circuit 
together. Vary the resistance in the rheostat till the 
needle shows a deflection, for example, of 45 degrees. 
Then, referring to the table of tangents, we find that 
the tangent of 45 degrees is 1. Note the resistance un¬ 
plugged and find what half of the tangent of the deflec¬ 
tion is. In this case, as the tangent is 1, its half will be, 
of course, one half, or, in decimals, .5. Referring again 
to the table, we see that the degree of which .5 is the 


ELECTRICAL MEASUREMENTS. 


121 


tangent is 27. Then unplug resistance until the deflec¬ 
tion is reduced to 27. Again note the resistance un¬ 
plugged. Then, to ascertain the battery resistance, 
double the smaller resistance noted and add to the re¬ 
sult the resistance of the galvanometer, and subtract 
the total from the larger resistance. The difference is 
the resistance of the battery. For example : We use a 
galvanometer of 100 ohms resistance, and unplug for the 
first deflection 80 ohms. To halve the tangent of the 
first deflection we have to unplug 400 ohms. We then 
double the smaller resistance, the result being 160 ohms, 
to which we add the resistance of the galvanometer, 100 
ohms, making in all 260. Then we subtract 260 from 
the larger resistance unplugged, 400 ohms, and find that 
the difference is 140, which is the resistance of the bat¬ 
ter v. 

A third method is to join two cells of the battery 
whose resistance is to be measured in opposition to one 
another, so that they send no current of their own, and 
then measure the two together by a tangent or differen¬ 
tial galvanometer, in the same way that we would mea¬ 
sure any other resistance. 

The resistance of a single cell will be half of the two. 

114. How is the resistance of a galvanometer ascertained % 

If we have more than one galvanometer at hand the 
obvious way of ascertaining the resistance of either is, of 
course, to regard them as any other ordinary resistance 
to be measured, using one of them as an instrument with 
which to measure the other. But circumstances some¬ 
times occur which render it desirable that we should know 
the resistance of the galvanometer which we are using 
when we have no other to use as a measuring instrument. 
There are several ways wdiereby this may be accomplish¬ 
ed. The two simplest are here given : First, using the 
Wheatstone bridge. The galvanometer is placed in one 
of the branches of the bridge—branch 4, for instance— 
instead of being left in the cross-wire circuit as usual; 
and in the regular place of the galvanometer a circuit- 


122 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

closing key is placed, so that we may connect or discon¬ 
nect the two points which would ordinarily be connected 
to the galvanometer. The battery is retained in its 
regular position ; and, of course, the current flowing 
from it passes through the branches of the bridge and 
causes the galvanometer-needle to deflect. 

The coils in the other branches are then adjusted until 
the deflection remains unaltered, whether the key in the 
cross-wire is depressed or not. When this is the case a 
balance has evidently been effected, and consequently we 
get the resistance of the galvanometer by the usual pro¬ 
portion ; thus, as branch 1 is to branch 2, so is the resis¬ 
tance of branch 3 to the resistance of the galvanometer 
in branch 4. To illustrate: If we have 100 ohms un¬ 
plugged in branches 1 and 2, and to effect a balance 
we have to unplug 250 ohms, the first two branches be¬ 
ing equal, the galvanometer in branch 4 is also equal to 
the amount unplugged in branch 3—that is, 250 ohms. 
That this method may be clearly understood, we must 
go back for an instant to the principle of the bridge. 

We will see that if a balance is not established, and 
a current is flowing in the coils of the galvanometer, 
which is in its usual place in the cross-wire circuit, the 
current will be denoted by the deflection^of the needle ; 
and, as a matter of course, any change in the resistance 
of the galvanometer, or of any part of the cross wire, 
will affect the strength of current in all of the four 
branches of the bridge. If, on the contrary, a balance 
is established, and the fact is indicated by the needle re¬ 
maining undefiected, we may alter the resistance of the 
galvanometer, or even take it away altogether, without 
in any way affecting the current in the branches. 

So, in measuring the resistance of the galvanometer 
by this method, when equilibrium is once attained, it 
matters not whether the key in the cross-wire is open or 
closed, the deflection remains stationary. 

It will be observed that this measurement is identical 
in principle with one of the plans of measuring the in- 


ELECTRICAL MEASUREMENTS. 


123 


ternal resistance of a battery. As described in that 
method it frequently happens that the deflection of the 
needle is so great as to be immeasurable, and one of 
several expedients must be adopted to reduce it. 

This may be done by giving the needle an initial bias 
to one side by means of a permanent bar magnet, or, 
what is equivalent, bringing the needle back to zero by 
approaching the permanent magnet to it. 

Or we may shunt the galvanometer by a shunt of suf¬ 
ficiently low resistance to bring the needle to a proper 
deflection, and then measure the joint resistance of 
shunt and galvanometer. 

Or we may shunt the battery, so that but a small part 
of the current passes through the galvanometer. 

Or we may weaken the battery current by inserting 
high resistance in the battery circuit. 

Or we may insert resistance in the same arm as the 
galvanometer, and, measuring the whole as one resist¬ 
ance, deduct the amount of the added resistance from 
the total to give the resistance of the galvanometer. 

The second method may be adopted when the bridge 
cannot be used, and is as follows : Put the galvanometer 
in circuit with a resistance-box and a battery whose in¬ 
ternal resistance is so small that it may be neglected; 
unplug any resistance, say 400 ohms, and note the de¬ 
flection. We will assume it to be 20 degrees. Then put 
plugs back, withdrawing resistance from the circuit un¬ 
til the former deflection is doubled, so as to reach 40 
degrees, there being then 300 ohms unplugged. Then 
multiply the two resistances by their respective de¬ 
flections, subtract the smaller product from the lar¬ 
ger, and divide the result by the difference between the 
two deflections. Thus, 400 ohms multiplied by 20 is 
8,000 ; and 300 multiplied by its deflection 40 is 12,000. 
Then 12,000 minus 8,000 leaves 4,000. That amount 
divided by 20, which is the difference between the de¬ 
flections 20 and 40 degrees, gives us, as the resistance of 
the galvanometer, 200 ohms. 


124 ELECTRICITY, MAGNETISM, AAD TELEGRAPHY'. 


115. How may the electro-motive force of batteries be mea¬ 
sured, compared, or estimated i 

The electro-motive force of a voltaic battery may be 
determined by several methods, blit as no absolute stan¬ 
dard of electro-motive force is known we cannot deter¬ 
mine the force of any particular battery in standard 
units (volts), but can only compare the relative force of 
two or more batteries. We will consider several of the 
most simple and reliable methods: 

First. If we join up a number of cells in circuit in 
opposition with a number of other cells and a galva¬ 
nometer, by adjusting the number of cells so that no 
current passes, and that, consequently, the needle lias 
deflection, the relative force of the two batteries may be 
determined. 

For example: We desire to know the electro-motive 
force of a chromic-acid battery of 10 cells, and we have 
a Daniell battery with which we can compare it. We 
know that a Daniell cell in good order is about 1.079 
volts. We connect one pole—the zinc, for instance— 
of our chromic-acid battery to one terminal of the gal¬ 
vanometer, and the carbon pole to the copper pole of a 
battery composed of an equal, number of Daniell cells ; 
the zinc pole of the Daniell battery is connected to the 
other terminal of the galvanometer. We then find that 
the chromic-acid battery causes the needle to deflect. 
We add cells to the Daniell battery until the needle de¬ 
flects no longer. We find that we have added 10 cells. 
Thus it has taken 20 Daniell cells to balance 10 of the 
chromic-acid cells, showing that the chromic-acid bat¬ 
tery has just twice the electro-motive force of the Dan¬ 
iell, or in the ratio of 2 to 1. 

To ascertain the value in volts multiply the electro¬ 
motive force of the Daniell cell, 1.079, by the number 
of cells, 20, and divide by the number of acid cells, 10. 
The quotient is 2.158, which is the value of the chromic- 
acid cell; or, in other words, as the larger number of 

cells is to the smaller number, so is the electro-motive 

\ ' 


ELECTRICAL MEASUREMENTS. ‘ 125 

force of tlie larger number, in volts, inversely to tliat of 
the smaller number. 

llie second method, using a tangent galvanometer, is 
as follows : The electro-motive forces of two batteries, 
which we will call No. 1 and No. 2, are to be compared. 
No. 1 is joined up in circuit with a galvanometer and 
a resistance-box. Sufficient resistance is unplugged to 
cause a convenient deliection of the needle. The tan¬ 
gent of the deflection must be noted, as must also the 
total resistance in circuit—that is, the resistances of the 
battery, galvanometer, and that unplugged from the box. 
Then remove battery No. 1 and substitute No. 2. If 
the internal resistance of No. 2 is different from No. 1, 
the resistance unplugged must be adjusted until the 
total resistance in circuit is the same as before. Again 
note the tangent of the deflection. Then the electro¬ 
motive force of No. 1 is to the electro-motive force of 
No. 2 as the first tangent noted is to the second. 

For example: Let No. 1 battery have a resistance of 
60 ohms and the galvanometer 100 ohms. We unplug 
800 ohms in the resistance-box, making a total resistance 
of 960 ohms. 

With this resistance we will suppose the needle de¬ 
flects to 35 degrees. Referring to the table of tangents, 
we find that the tangent of 35 degrees is .70. 

We note the above facts and disconnect battery No. 
1, substituting in its place No. 2, which lias a resistance 
of 100 ohms. We alter the resistance-coil to 760 ohms 
to make the total resistance the same as before—that is, 
960 ohms. We find the deflection now to be 42 degrees, 
the tangent of which is .90. 

Then as .70 is to .90, so the E. M. F. of No. 1 is to the 
E. M. F. of No. 2. In these measurements it is supposed 
that we know the E. M. F. of one of the batteries, which 
is called the standard battery ; so, to reduce the calcula¬ 
tions to figures, we will call No. 1 the standard, and as¬ 
sume it to have a value of 20 volts ; and as .70 is to 20 
volts, so is .90 to 25f volts. 


126 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

The third method was devised by Wheatstone, and 
consists in placing each battery alternately in circuit, 
varying resistance to produce the same deflection with 
each, then adding the required resistance in both cases 
to produce lower but, again, similar deflections ; the 

E. M. F.s then being directly proportional to the added 
resistances which in both cases were required. 

To illustrate: No. 1 battery, which we will suppose 
has a known E. M. F. of 25 volts, is placed in circuit 
with a galvanometer and a resistance-box. We unplug, 
say, 2,000 ohms, and note the deflection to be 30 degrees. 
Adding 200 ohms to that already unplugged brings the 
deflection down to 24 degrees. Taking out battery No. 
1 and inserting battery No. 2, we And that to produce 
the same deflection—30 degrees, as at first produced 
with No. 1—we have to unplug but 1,800 ohms ; and 
by adding 150 ohms we bring the deflection down to 
that produced by adding, when N o. 1 was in circuit, 24 
degrees. Now, the amount added in the measurement 
of No. 1—that is, 200 ohms—is to the amount added in 
the measurement of No. 2—viz., 150 ohms—as the E. M. 

F. of No. 1, 25 volts, is to ISf volts, the E. M. F. of 
No. 2. 

116. What is a shunt i t 

A shunt may be defined as a contrivance for leading 
by another route part of a current which, as a whole, 
is too powerful for the immediate purpose. In the pre¬ 
sent connection it is a coil of wire used to divert some 
definite proportion of a current aside from or past a gal¬ 
vanometer or other instrument, instead of allowing it to 
t pass through the instrument coils. 

For instance, if the galvanometer lias its two terminals 
connected by a wire which includes a resistance equal 
to one ninety-ninth of the resistance of the galvanome¬ 
ter, we reduce the galvanometer to one-hundredth of its 
original sensibility, ninety-nine hundredths of the cur¬ 
rent passing through the shunt and the remaining hun¬ 
dredth through the galvanometer. Similarly, if the 


ELECTRICAL MEASUREMENTS. 


127 


sliunt be exactly equal to the galvanometer the current 
will divide in equal proportions between the galvanome¬ 
ter and the shunt. If the shunt is one-half the resist¬ 
ance of the galvanometer, two-thirds of the current will 
pass through the shunt and one-third through the gal¬ 
vanometer, and so on. The rule is that the current di¬ 
vides between the galvanometer and the shunt in inverse 
proportion to their respective resistances, the greater 
portion of the current always going through the smaller 
resistance, and the smaller portion through the greater 
resistance. 

When very strong currents are being used in measure¬ 
ments it is necessary that a shunt be employed, in order 
that the needle’s defections may be reduced to a reason¬ 
able limit. 

Galvanometers are usually provided with three shunts, 
which are respectively one-ninth, one ninety-ninth, and 
one nine-hundred-and-ninety-ninth. These reduce the 
current passing through the galvanometer respectively 
to its one-tenth, one-hundredth, or one-thousandtli part. 

117. What is the formula for finding what resistance a shunt 
should be to reduce the sensibility of a galvanometer to any re¬ 
quired fractional part , and what is meant by the multiplying 
power of a shunt t 

The formula for finding what the resistance of a shunt 
should be, to give it a definite value, is to make the re¬ 
sistance of the shunt equal to the resistance of the gal¬ 
vanometer, divided by the multiplying power required, 
minus 1. 

For example : Suppose we have a galvanometer whose 
resistance is 100 ohms, and we wish to prepare a shunt 
which will reduce the sensitiveness to one-tenth. We 
divide the galvanometer resistance by the fractional part 
to which we wish to reduce the sensibility, minus 1— 
that is, we divide the 100 by 10, minus 1, which is, of 
course, 9. The quotient of 100 ohms divided by 9 is 
111 ohms, which is the resistance of the shunt re¬ 
quired, and is one-nintli of the resistance of the galva- 


128 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

nometer. This is called a shunt having a multiplying 
power of 10. To obtain the true value of a deflection 
taken, for instance, from a shunted tangent galvanome¬ 
ter, we must multiply the tangent by the multiplying 
power of the shunt used. To ascertain the multiplying 
power of any shunt whose resistance is known we di¬ 
vide the resistance of the galvanometer by the resistance 
of the shunt, and add one to the quotient. 

Again : We are using a galvanometer with a resist¬ 
ance of 100 ohms, and insert a shunt whose resistance 
we know to be 25 ohms. To find out by what num- 
ber we have to multiply the shunted result we divide 
the 100 by 25, which gives us a quotient of 4, to which 
must be added 1, showing that 5 is the multiplying 
power required. 

118. If we employ a shunt of a given proportion , is the cur¬ 
rent which then passes through the galvanometer strictly the 
proportionate part of the original current to which it is appa¬ 
rently reduced l 

]N"o ; because by the act of employing the shunt we 
furnish a double route for the current, and thereby 
diminish the external resistance of the circuit, and, 
as a consequence, the strength of current furnished by 
the battery is increased. It is, therefore, the increased 
current that splits between the shunt and the galva¬ 
nometer, instead of the original one. For example : If 
we are using a tangent galvanometer, and the tangent of 
deflection without the shunt is .80, we might naturally 
have supposed that, on the introduction of a shunt which 
reduces the sensitiveness of the galvanometer one-half, 
the tangent would also be brought down one-half—that 
is, to .40. But such is not the case, the result being 
some higher tangent than .40 ; and to bring about an 
accurate result we must first find the joint resistance 
of the shunt and galvanometer, and then insert an ad¬ 
ditional resistance in the battery circuit equal to the 
amount by which the original resistance was decreased. 
Thus, if both the galvanometer and shunt are 100 


ELECTRICAL MEASUREMENTS. 


129 


ohms resistance, the joint resistance of the two is 50 
ohms. 

In this case, therefore, we should have to insert 50 
ohms in the battery circuit to compensate for the de¬ 
crease in resistance and to bring the current back to 
its original strength. 


CHAPTER X. 


PRINCIPLES OF TELEGRAPHY EXEMPLIFIED IN DIFFER¬ 
ENT SYSTEMS. 

119. What are the necessary parts of every line of telegraph , 
or telegraphic circuit i 

In answering tills question we shall be assisted by re¬ 
membering wliat is the work required to be done in elec¬ 
trical transmission. 

This, we shall see, may be divided into three heads : 
First. To generate or develop the electricity in sufficient 
quantity and of the necessary strength to do the re¬ 
quired work in the circuit. Second. To be able to trans¬ 
mit the electricity to any required distance without any 
serious loss by the way. Third. To cause it, on its 
arrival at the distant point, to produce results appre¬ 
ciable by the senses ; in other words, to record or de¬ 
liver its messages. 

To accomplish these results, then, it is necessary to 
have in each telegraphic circuit-, as shown in Figure 50— 


LINE 



(1) A generator of electricity, which in nearly every 
case is a galvanic battery, E, but which may be, and 
sometimes is, a magneto or dynamo-electric machine. 

(2) A conductor of electricity between the stations 
A and B, consisting usually of an insulated line-wire 

130 











PRINCIPLES OF TELEGRAPHY EXEMPLIFIED. 131 


extended from one terminal station to tlie other, and 
ending in the ground, G, at each terminal. 

For practical purposes the earth may be regarded as 
a return wire. A\ hen the line is a short one a return 
wire is often actually used, and is indeed preferable, as 
the earth connections frequently interpose a higher re¬ 
sistance than a short return wire. 

(3) At each station apparatus to render the current 
evident to the senses—that is, instruments, M and M', 
wherewith to receive the signals and to interpret them, 
and corresponding instruments, K and K', by which 
they are transmitted. 

These elements— i.e., the battery, the line-wire, the 
transmitting and receiving instruments at each station, 
and, finally, the earth—compose the telegraphic circuit. 

120. Have any attempts been made to utilize frictional elec¬ 
tricity for telegraphic purposes t 

Yes, in several cases. The first attempt on record is 
that of Lesage in 1774. He employed twenty-four 
wires, one for each letter in the alphabet, each wire 
terminating in a pitli-ball electroscope, tagged with its 
respective letter. Then Lomond, in the year 1787, em¬ 
ployed one wire, with a pith-ball electroscope. In the 
same year Betancourt used one wire, operated by a Ley- 
den-jar battery. The next attempt was made by Reizen 
in 1794. He arranged twenty-six wires. The letters 
were cut out in tin foil and rendered luminous by the 
passage of the electric spark. In the next year Cavallo 
used one wire, and the number of sparks designated 
the different signals ; two hundred and fifty feet was, 
however, the extreme length of line he used. In 1796 
D. F. Salva, of Spain, is said to have worked a tele¬ 
graph through a line of twenty-six miles. 

In 1816 Ronalds laid wires both underground and in 
the air, and used a pith-ball electroscope hung in front 
of a clock, which enabled the letters on a dial to be read 
off. Finally, Harrison Gray Dyar, an American, con¬ 
structed a telegraph on Long Island, in 1827 and 1828, 


132 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


which was to represent the different letters by means of 
the difference in time between the several sparks. In 
all these systems frictional or mechanical electricity was 
intended to be employed. These early attempts in elec¬ 
tric telegraphy, valuable as successive steps in the art, 
were all failures, chiefly from the fact that frictional elec¬ 
tricity, from its high potential, or, in other words, its 
great power of overcoming resistance, escapes from the 
line of communication over even the poorest conductors. 

121. What systems of commercial telegraphy are in use at the 
present time i 

In America the telegraphs now in general use are : 

1. The Morse, with its improvements of duplex, quad- 
ruplex, and harmonic telegraphy ; its use is universal. 

2. The type-printing telegraph, used chiefly on trunk, 
lines between Boston and New York, New York, Phila¬ 
delphia, and Washington, and New York and Chicago. 

3. A variety of the automatic system, known as the 
“ Rapid ” telegraph. 

4. The Wheatstone automatic system. 

In nearly every country the Morse system is mostgene- 
erally used, and maintains its supremacy on account of 
its simplicity, its comparative accuracy, and the speed 
with which it may be manipulated. 

The AVlieatstone needle system is still employed on 
many circuits in England, but is being gradually super¬ 
seded by the Morse. 

Its use is advocated by English telegraphic authorities 
for circuits which have many stations, none of which 
singly do much work, but which collectively have 
enough business to occupy a wire, and for railroad 
service. The maintenance of the needle system is eco¬ 
nomical. 

A magneto-dial system, called the Wheatstone A B 
C, is also extensively employed there, and is especially 
adapted for branch lines and offices in small villages 
where there is not enough work to pay for an expert 
operator, the Wheatstone automatic is also much used. 


PRINCIPLES OF TELEGRAPHY EXEMPLIFIED. 133 

Indeed, England lias been most successful in automatic 
telegraphy. 

122. Give a brief outline of the American closed-circuit Morse 
telegraph system. 

A number of stations, each provided with main line 
instruments, consisting of a key and relay, together with 
local circuit instruments, consisting of a sounder or re¬ 
gister and a local battery, are placed on one main circuit 
together. The main line may be of any desired length 
within certain limits, but is not ordinarily more than two 
or three hundred miles long. The two end stations are 
called the terminal stations, and at these the main bat¬ 
teries are usually located. Should it take three hun¬ 
dred cells of battery to work the line, about half should 
ordinarily be placed at each end. In that case, if at 



one terminal station the copper pole of the battery be 
to line, at the other terminal station the zinc pole must 
be to line ; and the circuit, starting, we will say, at sta¬ 
tion A, at the ground, will pass through the battery of 





















134 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

one hundred and fifty cells, entering at the zinc pole y 
leaving the copper pole for the line. 

Thence its route is from station to station, at each one 
passing through the spools of the relay and the key, 
until it arrives at the distant terminal, station B, where, 
after passing the relay and key, it enters the battery at 
the zinc pole and finally leaves its copper pole for the 
earth. A great number of stations may be included in 
this main circuit, and all the instruments will work 
simultaneously in unison with each other when a key is 
operated at any station. This arrangement is clearly 
shown in Figure 51. 

Should an operator at any office wish to send a mes¬ 
sage to any other office, he must open his key, thus 
breaking the circuit and causing the current to be inter¬ 
rupted. The armature of each relay in the circuit then 
falls away, opening the local circuits and causing the 
sounder or register armatures to respond in a similar 
manner. 

The operator then manipulates his key by alternately 
depressing it and allowing it to rise so as to form the let¬ 
ters of the Morse alphabet. The armatures of all the 
relays and sounders in the circuit respond to each of his 
movements, and so convey the desired signals throughout 
the entire circuit, including the distant station. 

The electrical arrangement of a terminal station is 
shown in Figure 52, in which the line, L, enters the sta¬ 
tion by the lightning-arrester, X, passes to the relay, M, 
which it enters by the binding-screw 1 and leaves by 
the screw 2, proceeds to the key, K, and from thence by 
the main battery, E, to the ground (4. 

The relay operates the circuit of the local battery, E', 
which, leaving the positive pole of the battery, is led to 
screw-post 3 of the relay, through the armature and cir¬ 
cuit-closing points of the same to screw-post 4, out to 
the sounder, S, and from thence back to the negative 
pole of the local battery. 

The arrangement of a way station is quite similar y 


PRINCIPLES OF TELEGRAPHY EXEMPLIFIED. 135 


differing only in the fact that the main wire, after pass¬ 
ing the relay and key, instead of going to the main bat¬ 
tery and ground, leads out to the next station. A cut¬ 
out is necessary at way stations. 



the main line is illustrated by Figure 53, where a relay, 
M, in a main-line circuit is shown, provided with an ar- 



Fig. 53. 

mature and lever, S. This forms part of the circuit of a 
local battery, B, which passes through the relay-points, 
P, and sounder-magnet, G; the points actually having 





















































136 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

the same functions as a key, but being automatically 
worked by the attraction of the relay. 

123 . Why is it that , as just stated , the batteries in a Morse 
telegraphic circuit are usually placed at the terminal stations i 

It is usual to place half the battery at each end of the 
line, because, as all lines are more or less liable to defec¬ 
tive insulation, such an arrangement tends to give better 
results on the whole than if the battery power were all at 
one end. If the battery were so placed, and the insula¬ 
tion at all imperfect, the working current, on account of 
the leakage, would be much weaker at the distant end 
than at the battery end. 

124 . Is electric telegraphy used for any other than commercial 
p urposes i 

Yes, it is employed for a great variety of different pur¬ 
poses. In contradistinction to commercial and railroad 
telegraphy—which is properly restricted, in its meaning, 
to the sending and receiving of messages—systems for 
other and distinct purposes are here called special sys¬ 
tems. 

«—4 _ 

125 . What are the principal special systems used in America t 

The municipal lire-telegraph system, the District or 

messenger business system, the police telegraph, the 
Gold and Stock or Exchange printing telegraph, and 
the automatic fire-signalling ^system. 

126 . Describe in general terms the construction and operation 
of the municipal fire-telegraph. 

The fire-telegraph system of America has repeatedly 
proved its great value, and is a well-known American 
institution. It has been brought to a state of great per¬ 
fection by the Gamewell Company. 

The lines all radiate from a central point, connecting 
with a number of signal boxes in various parts of the 
city. They are uniformly what are termed metallic cir¬ 
cuits, the ground forming no part of the circuit; that is, 
the line, leaving, for example, the copper pole of the bat¬ 
tery, after making its circuit of the city returns by an¬ 
other route to the zinc pole of the battery. 


PRINCIPLES OF TELEGRAPHY EXEMPLIFIED. 


137 


In large cities tlie signals transmitted from the boxes 
are carried by the wires to a central office, from which 
the alarm is given to the engine-houses and other neces¬ 
sary points. 

The action of the signal-boxes is as follows : When 
the handle is pulled, a detent is tripped, which permits 
a circuit-wheel to revolve by a train of clock-work, and 
so to break the circuit a given number of times, thereby 
giving the required signal. Portions of the edge of the 
wheel are made of non-conducting material, and a metal¬ 
lic spring, which forms part of the circuit, presses on the 
edge of the wheel. When, therefore, the insulated por¬ 
tions pass under the spring the circuit is broken. It 
will be seen that by altering the relative number and 
position of the non-conducting portions of rlie edge of 
the wheel any required specific arbitrary signal may be 
given. 

The circuit being thus closed and broken by the re¬ 
volution of the wheel under the spring, the armature of 
a relay is correspondingly attracted to and withdrawn 
from its magnet at the central office, and when falling 
back closes a local circuit and strikes the signal on a 
bell, at the same time recording it on a register. The 
operator then repeats the signal to every required point 
in the system, and the alarm is given. In smaller 
places, although the operation of the boxes is the same, 
the alarms when sent in are automatically made known 
to the proper parties and to the public by automatic re¬ 
peaters, which set in action bell-strikers at prearranged 
points. The attendance of an operator is thus rendered 

unnecessary. 

•/ 

127. Describe briefly the District system of telegraphy. 

This system has been for several years a great con- 
«/ 

venience in our cities, and its electrical department is 
simplicity itself. 

The circuits, like those of the fire-telegraph, are metal 
lie, leaving one pole of the battery in the district office, 
running to a number of boxes placed at the residences 


138 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

and places of business of subscribers, and returning by 
another route to the other pole of the battery at the 
office. The boxes are virtually small models of those 
used for fire service, and consist essentially of a me¬ 
tallic break-wheel and contact-spring, both of which 
form part of the circuit. When the wheel rotates the 
circuit is closed and broken, and the signal correspond¬ 
ingly given. Different signals may be sent by the same 
box by different manipulation. For example, if a box 
signal was 29, 29 once transmitted may signify that a 
messenger was wanted ; twice, a call for a policeman, 
and so on. The signals are given by the back stroke of 
a relay closing a local circuit, embracing a local battery- 
register and a single-stroke bell. The register records 
the signal on its strip of paper, and it is simultaneously 
struck on the bell. 

Each subscriber is represented in the office by tickets 
bearing his number, so that no time is lost in ascertain¬ 
ing from whom the"signal is sent. The batteries used in 
this system are generally of the gravity form, and are 
not usually very large, as the entire external resistance 
is not great, the relay being the only electro-magnet at 
all times in the circuit. If a line breaks, or disconnection 
from any cause takes place, the break is first localized, 
and until it can be repaired, a ground connection is at¬ 
tached at the nearest box on each side of the trouble, so 
as to complete the circuit through the earth. If an ac¬ 
cidental connection with the ground should occur, or, as 
it is technically said, a ground appears on the wires, 
it is at once tested for by grounding the circuit at the 
office, and opening or sending signals from various boxes 
on the circuit. Each box between the office ground and 
the fault will, when operated, send in its signal, while 
the boxes beyond the fault will not, they being short- 
circuited or cut off by being between the fault and the 

office on the other side, so that neither the relay nor 

*/ 

battery is in circuit with them. As soon as the ground 
is localized, it should be removed, because if another 


PRINCIPLES OF TELEGRAPHY EXEMPLIFIED. 139 

ground should appear the effect would be the same as 
that just indicated—that is, all stations between the two 
grounds would be cut out. 

128 . JMicit is usually the system of police telegraph t 

There is no system especially devoted to police inter¬ 
communication, each city possessing such a system 
using that which, in the eyes of its municipal authorities, 
appears to be the best. 

In New York a dial telegraph, worked by a step-by¬ 
step motion, is employed, wherein a pointer or index- 
hand travels round a dial marked with the letters of the 
alphabet and the cardinal numerals. Each time the cir¬ 
cuit is broken and closed the pointer advances one let¬ 
ter. This system is very popular, on account of the 
economy of maintenance and the ease with which it is 
worked. 

129 . Describe in a general manner the system of the Exchange 
printing telegraphs. 

The Exchange printing telegraph is also essentially 
an American institution, and may now be said to be a 
necessity among the stock, cotton, and produce brokers 
of our large cities. The entire business has grown up 
since 1867. Anything of the nature of a com]ffete his¬ 
tory of the business, or any details beyond a general 
description of its operation, would be out of place 
here. 

The quotations of the market prices of stocks, cotton, 
and produce are collected from the various exchanges 
and transmitted, from the office or central operating- 
room, over a great number of wires to the offices of the 
subscribers. Information regarding interesting events 
and general news of the day is also gathered and fur¬ 
nished by special circuits arranged for that purpose. In 
the place of business of each subscriber is a portable 
printing instrument which prints the communications 
in plain Roman type. Many styles of printing instru¬ 
ments have been tried, but they may be all resolved into 
two classes : first, those operated by the mechanical 
make and break of the circuit; and, second, those ope- 


140 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


rated by electrical pulsations of alternate positive and 
negative direction. 

An instrument of each character will here oe briefly 
described. 

The most generally used instrument of the first class, 
on account of its simplicity of operation, is what is 
technically known as the kt three-wire stock" instru¬ 
ment, which is, as its name indicates, operated by three 
distinct wires, one of which influences the alphabetical 
type-wheel, another the numerical type-wheel, and the 
third operating the press magnet and printing the quo¬ 
tations. The transmitting device is alternately switched 
to the alphabet and figure wire ; and whenever the type- 
wheels are brought to the required letter or figure the 
press-wire is placed automatically in the battery circuit 
and the impression given. 

The wheels are operated by a step-by step propelling 
escapement, each one on its own arbor, on which is also 
fixed a star wheel, which is advanced by a lever and pal¬ 
lets attached to the magnet armatures. 

The armature-levers are both retracted by strong 
springs, and the star wheels are so placed that each 
time the armatures are attracted the type-wheels are 
advanced one character, and each time they are with¬ 
drawn the wheels are advanced another character, so 
that work is done both by the charge and discharge 
of the magnets. The press magnet, by special me¬ 
chanism, causes the strip of paper to advance a cer¬ 
tain distance after each impression, so as to be ready 
for the next one. This instrument is much liked by 
the patrons, on account of the clear impressions and 
large type printed by it. 

The instruments of the second class mentioned are, if 
possible, still more simple in construction, though a lit¬ 
tle more complex in principle, than the machine already 
described. They require but one line-wire, and the type- 
wheel prints both letters and figures, being made suffi¬ 
ciently large to contain both. The type-wheel axis is 
driven by a clock-train operated by a weight or spring, 


PRINCIPLES OF TELEGRAPHY EXEMPLIFIED. 141 


and is controlled by an escapement, A, attached to a po¬ 
larized armature. This latter vibrates on pivots between 
the opposite X3oles of two electro magnets, T T, placed in 
the same circuit, facing each other, and both working the 
same polarized armature. Instead of being vibrated by 
the alternate opening and closing of the circuit, it is 
drawn from side to side by rapidly succeeding x>ulsa- 
tions of alternate polarity. That is to say, if one xiulsa- 
tion is sent from the x^ositive x^ole of the battery, the 
next is sent from the negative x>ole, and so on ; and each 
pulsation permits the tyx3e- 
wheel to advance one charac¬ 
ter. A third magnet, P, with 
a much longer core than the 
two already mentioned, is also 
in circuit, and is provided 
with an armature, whose lever 
presses ux3 the paper to the 
tyx3e wheel to print the im¬ 
pression. The rapidly altern¬ 
ating pulsations pass through 
this magnet, but its armature 
is not affected until a pause is 
made, because the alternately Fig. 54. 

opposite pulsations succeed 

each other so tepidly that the long magnet lias not time 
to become charged sufficiently to attract its armature, 
which is kex3t against its back-stop by a stiff spring. 
When, however, a current of either direction is kept on 
the line longer than usual, the armature is instantly at¬ 
tracted and the x>rinting performed. The movement for 
feeding the paper a ^ so performed by the armature- 
lever of the x^inting magnet. This instrument prints 
very rapidly. Both styles of instrument are placed in 
any required number on a circuit, and any number of 
circuits may, by relays or other contrivances, be oxie- 
rated by one key-board and ox3erator. 

Figure 54 is a diagram showing the principle of the 
latter instrument. 


























CHAPTER XI. 


VOLTAIC CIRCUITS. 


180 . What is an electrical circuit f 

The entire path of the electrical current, including the 
battery itself and the conducting medium which unites 
its poles. 

If we take a voltaic battery and connect its poles to¬ 
gether by a short wire, as in Figure 
55, the battery and connecting wire 
compose the circuit. If we take a 
battery, connect one pole to the earth 
and the other pole to a telegraph 
line-wire, say, one hundred miles in 
length, with ten relays, and at the 
end of the one hundred miles con¬ 
nect the line-wire to the earth, the 
battery, its earth-wire, the line-wire, 
the ten relays, and the earth itself compose the circuit. 

A circuit of which the earth forms a part is called an 
earth circuit. One in which a return wire is used, or of 
which the earth forms no part, is called a metallic circuit. 



Fig. 55. 


131 . Give a short history of the use of the earth as a part 
of the circuit. 

The discovery that the earth would serve as a con¬ 
ductor for the galvanic current is usually attributed to 
Steinheil, who. in 1837 and 1838, was experimenting on 
a German railroad, with the view, if possible, of using 
the rails as telegraphic conductors, and thereby dispens¬ 
ing with wires. He found that he could not sufficiently 
insulate the rails from each other ; he then used one insu¬ 
lated wire and rail, which proved to be a perfect success, 
the rail acting both as a ground and also as a direct con¬ 
ductor. And there is no doubt that to him is due the 

142 






















VOLTAIC CIRCUITS. 


143 


credit of making and first applying this practical sug¬ 
gestion, which had two great immediate advantages— 
viz., it halved the number of wires requisite, and on long 
lines doubled the strength of the working currents. 

But it is remarkable that the previous experiments of 
physicists in completing electrical circuits had not before 
1837 been utilized, as it is a fact that as early as 1746 
TV inckler, of Leipsic, used the river Pleisse to discharge 
Leyden jars. Le Monnier, of Paris, about the same 
date, made similar experiments. 

It was shown in 1747 by Watson that the earth could 
always be used as a part of the electric circuit, and his 
researches were verified both by Franklin and De Luc. 
These were, however, all researches in frictional or high- 
tension electricity : but in 1803 Basse, of Hameln, estab¬ 
lished the fact that the earth could be used as a part 
of a voltaic circuit. His results were verified by Erman, 
of Prussia, and Aldini in France, and finally Sbmmer- 
ing and Schilling experimented to the same end and 
with the same results in 1811. 

The apparent neglect of electricians to utilize this valu¬ 
able fact must have been due to an erroneous idea 
which they had permitted to take possession of their 
minds, that the earth could not be employed as a com¬ 
mon return ; in much the same way that the early en¬ 
gineers firmly believed that the locomotive could not run 
on smooth rails, and that toothed racks and spur-'wheels 
would be necessary. However, when the discovery was 
actually applied it was, and is still, justly regarded as 
one of the most important discoveries ever made in the 
art of electric telegraphy ; it is one which has largely 
contributed to the wonderful extension of telegraphic 
lines over the world. In long lines it is particularly 
valuable, as the resistance really offered by the earth 
and earth-plates is so small in proportion to that of the 
line that it may be regarded as practically nothing. 

The opinions of scientists differ as to the part the 
earth bears in the circuit, the older theory being that the 


144 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

current leaving tlie battery flowed along the line, thence 
to earth, and back through the earth to the other pole of 
the battery. The newer one, briefly stated, is that the 
earth is the common reservoir of electricity, into which 
the current from the battery flows. But whether the 
earth is or is not, properly speaking, a part of the cir¬ 
cuit, the fact remains that it can be used as if it were, 
which is the most essential point. 

132. On what conditions does the strength of current in a 
circuit depend t 

The strength of a current in any circuit depends upon 
the activity of the electro-motire force and upon the re¬ 
sistance which the electricity lias to overcome. 

If in a circuit of given electro-motive force and resist¬ 
ance we increase the electro-mot ire force , or if we de¬ 
crease the resistance , we increase the current strength. 
Conversely, if we diminish the electro-motive force or 
increase the resistance we reduce the current strength. 

It must be remembered that the resistance of a cir¬ 
cuit includes the resistance of the battery and the con¬ 
ducting wire ; also that the current strength is neces¬ 
sarily the same in every part of a circuit. The strength 
of current is measured or estimated by its power of de¬ 
flecting the magnetic needle, by its power of electrolysis, 
by its power of heating a wire of given thickness and 
material, or by the intensity of magnetism produced by 
it in an electro-magnet. 

133. How are batteries usually arranged for telegraph lines $ 

For telegraph lines the cells of a battery are nearly 



Fig. 56 


always arranged in series—that is, connected one after 
the other, as in Figure 56, the zinc of one being joined 
to the copper of the next, and so on ; because the great¬ 
est effective force of any battery is developed when the 
total external resistance equals the internal resistance of 







VOLTAIC CIRCUITS. 


145 


the battery, and, as it is generally out of the question to 
obtain such equality on telegraph lines, it follows that 
the best arrangement of the elements of a battery is that 
which most nearly approaches it. 

Haskins, in his work on the galvanometer, gives the 
following rule for proportioning a battery to telegraph 
lines : u Use two cups of Oallaud battery for each hun¬ 
dred units of resistance in the circuit. For example, 
suppose a line 200 miles long, Ho. 9 wire, 20 ohms 
to the mile. That is 4,000 ohms. Make the relays 
equal to it. For instance, 8 relays in circuit, 500 ohms 
each, which is also 4,000 ohms, making the total ex¬ 
ternal resistance 8,000 ohms. As for each hundred 
ohms, then, we use tAvo cups of battery, we divide 
the 8,000 by 50 and lind the quotient to be 160, which 
is the number of cells required.’’ 

It is very difficult to lay down any arbitrary rules for 
the proper proportionment of battery upon a circuit, as 
so much is dependent upon the size of the line-wire, the 
insulation, the earth-wires, and even the location of the 
line. Experience is the best guide in this matter, and 
the only one to be depended upon. 

As previously indicated, it is usual to place half the 
battery power of a line at each end, so as to reduce 
the effects of a possible escape. 

134 . Are batteries ever arranged differently from the manner 
described above ? 



Fig.- 57. 

Yes, they are sometimes connected side by side—that 
is, all the zincs are connected together to form one nega- 
tive pole, and all the coppers together to form one posi¬ 
tive pole, as shown in Figure 57. 


















146 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

Their electro-motive force is then no more than the 
electro-motive force of one cell, while the internal resist¬ 
ance is that of one cell divided by the entire number of 
cells, being, in fact, equal to one cell whose plates are as 
large as the combined plates of all the cells we have con¬ 
nected. In this arrangement the cells are connected to¬ 
gether to produce the largest amount of current through 
a circuit of very low resistance. 

135 . What rule is given for obtaining the greatest magnetic 
effect from a given battery t 

When the resistance of the coils of the electro-mag¬ 
net is equal to the resistance of the rest of the circuit— 
that is, of the conducting wire and battery—the magnetic 
force of the given battery is at its height. 

136 . Can more than one telegraph circuit be worked from a 
single battery i 

Yes; when the Grove battery, which has a very low 
internal resistance and very little tendency to polarize, 
was in general use in this country, as many as forty and 
fifty lines have been worked from it; and six or eight 
lines have been often worked by the carbon battery ; but 
the sulphate-of-copper batteries, which are now univer¬ 
sally employed, have too high an internal resistance to 
allow of more than two or three wires being worked 
from them. For this reason, when short telegraph lines 
are operated on closed battery circuits, One battery 
should never be made to supply more than three lines. 

The number of wires that can be worked in this man¬ 
ner, without interfering one with another, depends en¬ 
tirely upon the proportion between the internal resist¬ 
ance of the battery and the joint resistance of all the 
circuits connected with it. To get good results from 
this arrangement the battery must have a very low 
resistance, and the lines worked from it must be ap¬ 
proximately equal in resistance and equally well in¬ 
sulated. 

Under these circumstances, when several long lines are 
' connected with one common battery the strength of 


VOLTAIC CIRCUITS. 


147 


current is about equal on each. The explanation of this 
is that though, for instance, six lines of equal resistance 
are being supplied from one battery, and the current 
supplied by that battery is consequently divided among 
six conductors, and might, therefore, be supposed to fur¬ 
nish each line with a current of but one-sixth the strength 
that a conductor worked singly from the battery would 
have, such is not the case, owing to the fact that the ex¬ 
ternal resistance is diminished and is but one sixth of 
the resistance of a single line ; or, we may say, the sec¬ 
tional area of the conductor is increased six times, and 
consequently, we see by Ohm’s law, which has already 
been considered, the strength of current from the battery 
is increased, so that the loss which arises from the divi¬ 
sion of the circuit is balanced bv the gain resulting from 
the increased current, due to the reduction of the ex¬ 
ternal resistance. The battery, however, will become ex¬ 
hausted sooner than if it had but one line connected. 

The foregoing facts may be familiarly illustrated as 
follows : A large tank holding water has a pijie of an 
inch diameter leading out of it, through which the 
water flows. Suppose now that two more pipes of the 
same diameter are inserted ; a current of water equal to 
that flowing through the first pipe will flow through 
each of the other two pipes, because, though the water 
lias to divide itself between three conductors, the con¬ 
ductive capacity is increased, and consequently tlie vol¬ 
ume of water flowing from the tank is increased, the final 
result being that the water in the tank is more quickly 
exhausted. 

Several very weighty objections are made to the fore¬ 
going practice. One is that a battery fault affects all 
the circuits connected with it; another is that in wet 
weather, owing to the decreased resistance of the lines, 
they are apt to interfere with each other; and, in any 
case, there is no economy in working several lines from 
one battery, except in the matter of first cost of contain¬ 
ing jars and in the space occupied, because the con- 


148 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


sumption of material is in exact proportion to the work 
done. 


137 . Is there any rule that may he depended upon for propor¬ 
tioning battery power for short lines upon which signalling is 
effected by breaking and closing the circuit t 

No, there is no absolute rule that can be depended 
upon in all cases, as the strength of working current de¬ 
pends on several other conditions as much as on the 
battery. An imperfect ground-wire at the terminal sta¬ 
tion will often put so much resistance into the line as 
to destroy the effect of a sufficiently large battery. The 
safest plan in operating short lines—for example, a line 
one mile in length with six instruments in circuit—is, 
after constructing the line, to allow five cells of gravity 
battery for the mile of line, and add one cell for each 
instrument in circuit, making eleven cells in all. Then 
let the total resistance of the electro-magnets be equal 
to the total resistance of the line and battery. 

If the line-wire is No. 12 gauge, and is built of galvan¬ 
ized iron, its resistance'will be about 32 ohms, and the 
internal resistance of the battery, at 2 ohms per cell, 
is 22 ohms, a total of 54 ohms. The combined resistance 
of all the electro-magnets should then be also 54 ohms ; 
but to make the figures even we will call the electro¬ 
magnets 10 ohms each. 

The current will now, if the line is well constructed, 
enable the magnets to attract their armatures stronalv. 
If it is not strong enough one or two cells may be add¬ 
ed ; if too strong one or two cells may be taken from 
the battery. 


138 . To increase the strength of cur¬ 
rent in a given circuit should extra cells 
be added in series or should they be added 
in parallel circuit t 

It is well when placing a battery 
on a circuit, if the required battery 
power be unknown, to try first ’ a 
few cells in series, as in Figure 58 ; 
if these do not produce a current of sufficient strength, 



VOLTAIC CIRCUITS. 


149 




add more and more cells in series either until the current 
is strong enough or until the resistance of the battery is 
double that of the line. If the latter, at this point 
divide the battery into two equal parts, joining the cells 
in pairs, as shown in 
Figure 59. That is, for 
example, if the total 
number be sixty, divide 
it into two complete bat¬ 
teries of thirty cells 
each, and set these side 
by side, uniting the zinc poles of both to form one nega¬ 
tive pole, and the copper poles of the two batteries to 
form the positive pole. For this special number of cells 
this arrangement will give a current of exactly the same 
strength as when the entire sixty cells were joined in 
series. 

Noav, to increase the current add in pairs, at each ad¬ 
dition adding one cell in series to each row. 

To increase the current more and more this method 
can be readily continued until the whole number of cells 
employed is such that if all were joined in series their 
resistance would be six times the external resistance. 
When this point is reached, to increase the current still 
more the whole num¬ 
ber will have to be 
divided up and con¬ 
nected in three paral¬ 
lel circuits (see Figure 
60), after which addi¬ 
tions must be made in 
threes. The best re¬ 
sult in current from 
a definite number of cells can always be attained by 
adopting this method. 

139 . Are the results of working more than one line from a sin¬ 
gle battery more advantageous in short lines than in long ones t 

No, the advantages are even less. This may be clearly 



iii 


* l * i 1 1' i • 1 1 1 


'i' 


Fig. 60. 











150 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

illustrated in the following manner : We will first sup¬ 
pose that a line similar to that described in answer 53—• 
that is, a line resistance of 32 olnns and an instrument 
resistance of 60 ohms, making a total external resist¬ 
ance of 92 ohms—is satisfactorily operated by 11 cells of 
gravity battery. We will further assume that battery to 
have an electro-motive force of 11 volts and an internal 
resistance of 22 ohms ; the current on the line will, we 
see then, by Ohm’s law, be .09, or nine-hundredths of 
an ampere. 

We then add two other lines of equal total resistance, 
and find the amount of current on each line to drop to 
.07, as, though the current developed from the battery 
is increased to .21, it has to be divided between three 
conductors or outlets, which gives a result as stated 
above, an amount of .07 each. Now, to bring the cur¬ 
rent on each line up to the normal strength of the first 
circuit—that is ; .09—it will be found necessary to add 9 
cells of battery, nearly double the first amount, which 
shows how little economy there is, even in space occu¬ 
pied, in working batteries on this plan. Every evil re¬ 
sult which long lines so worked develop is shown and 
intensified in short lines. 

140. TT hat is meant by the expression “ joint resistance ” t 

The term joint resistance means literally the resist¬ 
ances of two or more independent branches of a circuit 
considered and treated as one. Thus if a battery is 
already provided with one wire, and a second is 
added of equal resistance, a second route is there¬ 
by provided for the current, and the result is ex¬ 
actly as if the first wire had been taken off altogether 
and replaced by one of exactty double the weight 
per foot. If still another wire of the same resistance 
is added the joint resistance is now but one-tliird of 
the original wire, as the conductivity is increased three¬ 
fold. It follows naturally that the resistance, which 
is the converse of conductivity, is lessened in the same 
proportion. 


VOLTAIC CIRCUITS. 


151 


141. What is the rule for finding the joint resistance of tivo 
or more parallel circuits i 

When the resistances of all of the circuits are equal 
there are three formulas, either of which may be em¬ 
ployed : 

First. Divide the resistance of one wire by the 
number of wires. For example, 5 wires each have 
a resistance of 60 ohms ; to obtain the joint re¬ 
sistance of the 5 wires we divide the 60 by 5, and, 
the quotient being 12, 12 is the joint resistance re¬ 
quired. 

Second. If there are only two wires divide the pro¬ 
duct of the respective resistances by their sum. Thus, 
2 wires each have the same resistance, 60 ohms ; 60 mul¬ 
tiplied by 60 equals 3,600 ; 60 plus 60 is 120; then divid¬ 
ing 3,600 by 120, we have as a quotient 30 ohms, which is 
the required joint resistance. 

Third. Divide the sum of the resistances bv the 
square of the number of the circuits. For example, 6 
circuits have a resistance of 60 ohms each. The sum of 
these resistances is of course 6 times 60, or 360, and the 
square of the number of circuits—that is, 6 multiplied 
by 6—is 36. Dividing 360 by 36, we find the result to 
be 10, which is obviously the joint resistance of the 6 
circuits. 

When the resistances of the circuits are unequal the 
following plan must be adopted: If only two wires, di¬ 
vide the product of the resistances by their sum as 
above. 

If the combined resistance of more than two circuits 
be required, first find the joint resistance of any two of 
them ; then, considering this as one resistance, combine 
it with a third, and so on. For instance, three wires have 
respectively the following resistances : 200, 300, and 100 
ohms. First take two of them : 200 and 300 multiplied 
together is equal to 60,000 ; 200 plus 300 is 500 ; then 
60,000 divided by 500 gives as the joint resistance of 
the first two wires 120 ohms. 


152 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

Now, calling that one circuit, we multiply 120 by 100, 
the resistance of the third wire, finding the product to 
be 12,000 ; 120 added to 100 being 220, we now divide 
the 12,000 by 220, which gives us as a result 54 and a 
fraction for the joint resistance of the three circuits. 




CHAPTER XII. 

LINE CONSTRUCTION. 

142. How may the conducting wires of telegraph lines be 
classified f 

They may be divided into three great classes, viz., 
aerial , subaqueous , and subterranean wires. The 
aerial lines may further be subdivided into those sup¬ 
ported on poles and those on house-top fixtures, the 
latter being cliiefiy employed in large cities. 

143. Under what heads may all materials for the construc¬ 
tion of the line be classed—the line here and hencefoadh to be 
understood as the conductor, regarded apart from the battery 
and instruments 1 

In the construction of a line of telegraph all the ma¬ 
terials employed may be comprised in one or the other 
of the following three heads: poles or other supports, 
wires, and insulators. 

144. Give some details concerning the choice and setting of 
poles. 

The poles used in this country are chiefly of white or 
red cedar or chestnut. Red cedar is the best, though 
the most unsightly, but chestnut is the most frequently 
used, especially in the Atlantic and Middle States. 

Poles should in all cases, when cut down, be cleared 
of all branches, stripped of their bark, shaved smooth, 
and then stacked for some time in such a manner that 
the air can freely circulate among them, so that they 
may be well seasoned. This is too often neglected, and 
poles are frequently set as soon as they are cut and 
trimmed. Very little is done for the preservation of 
poles used on American lines. The European telegraphs 
are far in advance of ours in this respect. In England 
the poles, before being set, are treated with solutions of 
metallic salts, which, being introduced into the pores of 

153 


154 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

the wood by different processes, combine with the sap 
and prevent decay. 

Poles should not be less than twenty-five feet long, 
nor less than five inches in diameter at the top. Their 
length must necessarily depend upon the number of 
wires they are to carry, but on the majority of trunk 
routes the length varies from twenty-five to forty-five 
feet. Except when passing through cities or towns they 
are rarely painted, although such a practice would con- 
duce to their longevity. 

They should be set at least five feet deep wherever 
practicable. The hole they are set in should be kept as 
narrow as possible, and perpendicular at one side, so that 
the pole will at least bear against one side of solid earth. 
When the earth is replaced it should be well tamped 
down after each few shovels are put in the hole, and mode¬ 
rate-sized stones may be tamped in close to the pole. 

All the cross-arms required should be attached before 
the pole is set, in order to save labor. The ordinary 
practice is to place them all on one side of the pole. The 
spaces cut for their reception on the side of the x>ole are 
called gains. 

In some cases cross-arms are not used, but brackets are 
employed, which are spiked to the pole, some on one 
side and some on the other, preferably alternating in this 
respect. It is a frequent practice also to bore a hole in 
the end of the pole and insert a pin which will carry an 
insulator, so that one wire may be strung on the top of 
the pole. Whenever this is done an iron ring, a little 
smaller than the top of the pole, should be heated red- 
hot and slipped over the end of the pole after the pin is 
driven in, to prevent the smaller end from splitting. 

The distance between the poles varies with the nature 
of the ground and must be left to the judgment of the 
constructor. But the number of poles to the mile will 
average about thirty, sometimes increasing to forty, and 
sometimes, on a straight and level road, decreasing to 
twenty. In this connection it may be well to observe 


LINE CONSTRUCTION. 


155 


that the fewer supports there are, the better the insula¬ 
tion, as each pole forms a branch circuit (of high resist¬ 
ance, it is true, but still a branch circuit) to the earth. 

In setting poles round a curve they should be made 
to lean back against the strain of the curve and should 
also be firmly guyed. 

145. Give information relating to the attachment of cross-arms. 

Cross-arms should be of white pine, well seasoned. 

They should also always be planed, bevelled off at the 
upper corners, and well painted. The length varies 
with the number of wires to be attached, while the or¬ 
dinary size of cross-section is four inches by five. In 
regular telegraph work the cross-arms are longer than 
in local or city lines. On a trunk line a cross-arm for 
two wares is about three feet long; for four wires, five 
feet six inches ; and for six wires, seven feet six inches; 
while the distance between the insulators from centre to 
centre is generally about twenty-tw r o inches. 

No such magnitudes are used on short private tele¬ 
graph or telephone lines, the cross-arms being much 
shorter in proportion and the insulators placed much 
nearer together. The cross-arms are fastened to the 
poles with either a pair of stout spikes or with lag- 
screws or bolts and nuts. The latter mode is preferable. 
All cross-arms should be fitted with the pins and insu¬ 
lators before the pole is set up. 

146. Describe the different supports in use for house-top lines , 
giving proportions of the same. 

These supports, which are technically called fixtures , 
are variously constructed, according to the character of 
the roof and locality where they are erected. They 
were, until within the last few years, of very simple 
construction and comparatively small size; but since 
the introduction of the telephone exchange systems 
they have necessarily increased in size, and it is a mat¬ 
ter requiring some mechanical skill to maintain the best 
proportions for strength and capacity. 

Two general classes comprise the whole—wall and 


156 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


roof fixtures. These, again, are made single or double, 
according to the number of wires they are required to 
support. 



A roof fixture is one which is placed on the actual 
roof of a building. 

A wall fixture is spiked to the side-wall of a building 
or a party-wall. 

A double roof fixture for telephone work should be 
made high, so as to clear all other wires. The upright 













































LINE CONSTRUCTION. 


157 



posts should be at least fifteen feet high and five inches 
square, the cross-bars fourteen feet long and four by 
five inches in thickness, and secured to the uprights by 
lag-screws. The upper cross-bar may be placed one foot 
from the top of the uprights, and the others eighteen 
inches apart. If but three are required instead of four, 
place them two feet apart. The insulators should be at 
least nine inches from 
centre to centre. All 
screws entering the 
roof should be care¬ 
fully soldered over to 
prevent leaks. 

In many cases it is 
preferable, and some¬ 
times even necessary, 
to use wall fixtures, as 
they remove all danger 
of causing leaks in 
roofs and are equally 
serviceable where roofs 
are pitched as when 
they are flat. The de¬ 
tails of this fixture are, 
in general terms, the 
same as those of the 
roof fixture just de¬ 
scribed. The upright 
posts have a total 
length of twenty feet, 
fifteen feet of which 
stand above the top of 
the wall, and the re¬ 
maining five feet are Flg - 62, 

used for fastening the structure to a piece of plank 
previously secured to the side of the wall. This plank 
should be five feet long, about ten inches wide, and two 
inches thick. It should be spiked to the wall with 



u 




u 
















































158 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

seven-inch spikes, and will then form a substantial base 
for the support of the structure carrying the wires. 
The upright posts and the cross-bars are the same size, 
and are arranged in the same manner, as those of the 
roof fixture. 

Where not more than a dozen wires run in one direc¬ 
tion they may be supported by single fixtures with one, 
two, or three cross-arms. The general directions given 
for double fixtures of the same class may be applied 

with equal propriety, 
and either the roof or 
wall fixture may be 
used as occasion may 
demand. The usual 
length of single roof 
fixtures is about twelve 
feet, and the size of 
stock five by live inches. 

Angle-irons are at¬ 
tached bv means of 
lag-screwy to the foot 
of the upright and to 
the roof. The fixture 
is firmly braced on 
three of its sides by 
rods of one and one- 
eiglith iron, hammered 
out at the ends, and 
fastened to the upright 
and to the roof by lag- 
screws. The first cross- 
arm is twelve inches 
from the top of the up¬ 
right, and the second and third eighteen inches from 
centre to centre. The two middle insulators are usually 
twelve inches apart, each of the others nine inches, and 
the outside insulators three inches from each end of the 



cross-arms. 























LINE CONSTRUCTION. 


159 


The same description applies equally to single wall 
■fixtures, except, of course, the method of attachment, 
which is similar in every respect to that of the double 
wall fixture. 

The usual insulator employed in house-top work is the 
glass insulator, either pony or standard size. Hook in¬ 
sulators are undoubtedly preferable i n every respect ex¬ 
cept cost. 

All fixtures, cross-arms, and boards should be of white 
pine and well painted. Spruce should never be used. 
House top fixtures should invariably be thoroughly 
guyed against lateral strain. 

If the wires pass in a straight line with the fixture 
there should be two guys placed, one on each side of the 
fixture, to hold it against the side-pressure produced by 
the wind acting on the wires. In case a section on one 
side of a fixture is longer and heavier than the section 
on the other side, a guy should be fastened to the fix¬ 
ture to pull against the strain produced by the heaviest 
section. In case the line makes an angle at the fixture 
the guys should be disposed so as to pull against the 
strain. For guy-wire use No. 9 galvanized iron. In 
arranging all guys the general principle should be re¬ 
membered that the fixture will simply hold up the line, 
and the guys must be strong and taut enough to resist 
all lateral or diagonal strain. Fixtures should not be 
more than from one hundred and fifty to two hundred 
feet apart. Sometimes when a single line is to be run 
light iron attachments are made use of, such as tripods, 
which, as their name indicates, are tliree-footed fixtures 
of round iron carrying an insulator on the apex of the 
triangle caused by the union at the top of the three legs. 
Ridge-pole fixtures and chimney-irons are other forms 
of light attachments which are more or less useful for 
light work. 

147. What is the use of insulators in telegraph or telephone 
lines 1 

The use of insulators on aerial lines is to prevent the 


160 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

loss of electricity at tlie points of support. They must, 
therefore, be made of some substance which is as nearly 
as possible a non-conductor. It is essential that the 
electricity should arrive at its destination as little di¬ 
minished in volume as possible, in order that it may 
thoroughly and easily perform its office. To this end 
the conductor must be insulated at every point of sup¬ 
port, both from the earth and from any other conduct¬ 
ing wire which may be on the same poles. 

The fact that some bodies offer very great resistance 
and that other bodies offer very little resistance to the 
passage of electricity lias rendered the electric telegraph 
possible. As all substances conduct in a greater or less 
degree, there is always more or less leakage to earth, 
and the working value of a telegraph line is the diffe¬ 
rence between the resistance of the insulators and the 
resistance of the conductor. It is, therefore, obvious 
that the better the insulation the better will be the opera¬ 
tion of the line. When a wire is carried through damp 
places, underground, or through water, the insulation 
has to be continuous and the wire must die covered with 
india-rubber or gutta-percha. 

148. What are leakage-conductors , and liow are they applied 
to pole lines f 

Leakage is a term applied to the escape of electricity 
from the wires in very small quantities. It is caused by 
imperfect insulation, which allows portions of the cur¬ 
rent to separate from its proper conductor and to divide 
itself between all the other roads to the ground, in pro¬ 
portion to their respective resistances. These other 
roads are, first, the pole ; and, second, the other wires, 
which are often of different lengths. So long as the 
current escapes to the earth no great harm is done, as 
the only effect is to weaken the signals ; but when it 
leaks into another wire it confuses the signals on the 
second line. The plan for remedying the trouble, first 
suggested by the English telegraph engineer Highton 
in 1S52, and subsequently patented by Varley in the 


LINE CONSTRUCTION. 


161 


United States, is to attach a thick wire to the pole, coil¬ 
ing the earth end in a spiral under the foot of the pole, 
and continuing the wire till it projects above the top 
of the pole, thus serving also as a lightning-conductor. 
Branch wires of a smaller gauge are then fastened to 
each earth-wire, and extended along the cross-arms to 
each insulator-pin, to which they are firmly attached. 
Any current then leaking from a wire will naturally 
take the quickest way to the earth down the poles met 
the earth-wires. This is most effective in preventing in¬ 
terference between wires when the eartli-wire is attached 
to every pole. The earth-wires, however, do more harm 
than good when they do not make a good earth connec- 
tion. A buried plate soldered to the earth-wire makes 
the best earth. 

Within the last few years improvements have been 
made in leakage-conducting appliances, which have 
taken the shape of metallic sleeves or sockets, fitted 
in the holes of the cross-arms in which the insulator-pins 
are inserted, and united with a continuous wire running 
from pole to pole and attached to the earth-wire of each.. 
The English insulators, being generally fixed on metallic 
pins, do not need these metallic sockets. 

Considerable attention has of late been given to this 
point, owing to the rapid increase of telephone lines, 
which, with their extremely sensitive instruments, render 
electrical disturbances of any character very evident. 

It is, however, still a question as to whether or not it 
is beneficial to apply these leakage-conductors to tele¬ 
phone lines of more than ten miles in length, on account 
of the increased electro static capacity acquired by lines 
furnished with them. The capacity is greatly increased, 
since the earth, by means of the ground-wires, is brought 
quite near to the lines ; and this increase in capacity 
tends to retard the currents made use of in telephony, 
and causes the spoken words to run together, thus ren¬ 
dering the articulate sounds transmitted undistinguish- 

able. 


162 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


149. In choosing insulators ivhat points should be considered f 

In the choice of an insulator the following conditions 
should be taken into consideration : 

The surface between the point where the line-wire 
touches and the substance of the pin-bracket or pole 
should be as long and also as narrow as can be attained. 

The material of which the insulator is composed 
should be as perfect a non-conductor as possible. 

The insulator should be of such a form that its ex¬ 
terior surface will be thoroughly washed by rain, yet 
that its interior surface shall not be reached by rain. 

It should have a surface which repels moisture. 

It should be strong enough to resist any strain likely 
to be brought to bear on it. 

It should be economical in first cost. 

There is, however, no insulator that combines all these 
virtues, and the best way is to choose that which com¬ 
prises the majority of them. 

Hard rubber is one of the best insulators, but soon 

loses its surface and be¬ 
comes rough and spongy 
when exposed to the 
weather. Glass, regarded 
simply as a non-conductor, 
is one of the best, but is 
objectionable from the fact 
that its surface has a great 
affinity for moisture and 
will be covered with a moist 
film in nearly every state 
of the weather. It is, how¬ 
ever, both cheap and con¬ 
venient ; and these consid¬ 
erations, in this country, so 
override all others that it 

is almost universally used. 

150. Describe some of the best or most generally employed 
insulators. 

The unprotected glass insulator, which is in almost 



























LINE CONSTRUCTION. 


163 


universal use in this country, naturally takes precedence 
with an American writer. It is generally made in the 
form represented by Figure 64. 

Though perhaps not so perfect an insulator in many 
respects as some others, its low price, more than fair in¬ 
sulating properties, and convenience of attachment en¬ 
able it to maintain its place in the front rank. 

As now made it has a screw-thread on the inside, 
by which it is secured to its supporting bracket or pin. 
The under side below the screw SAvells out, and the con¬ 
cavity thus formed keeps always a certain amount of 
dry surface and prevents an 
escape in wet weather. The 
line-wire is passed alongside 
the groove surrounding the 
insulator near the top, and is 
fastened with a tie-wire, which 
passes around the insulator, 
while both of its ends are 
twisted around the line-wire. 

The glass insulator with a 
wooden covering is used to 
some little extent in the 
United States. It is shown 
in Figure 65, and has no 
particular features except 
those indicated by its name. 

It is to be objected to chief¬ 
ly because when an insula¬ 
tor becomes defective it is 
a very difficult matter to 
discover the defect ; and, 
moreover, it has been ascer¬ 
tained that when such insu¬ 
lators are used the percentage of leakage is compara¬ 
tively high. 

Next comes the brown earthenware insulator, which 
is in general use in England. It is composed of two 



"Fig. 65. 










































164 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

separate cups, tlie smaller of which is fitted into the lar¬ 
ger, and is fastened by a cement consisting of equal 
parts of fine sand, cement, and plaster of Paris. The 
iron bolt is galvanized, and is fixed in the inner cup by 
another cement, which is composed of live parts of clean 
sand, three parts ashes from a locomotive fire-box, and 
two parts pine resin. A groove is formed on the upper 
part of the insulator, and in this the line-wire is bound, 
in a manner similar to the glass insulator. 

that sulphur is not a good 
insulator cement, as it 
splits the insulator, appa¬ 
rently by expansion. 

The Brooks insulator, 
Figure 66, is in many re¬ 
spects an excellent one, 
and gives very satisfac¬ 
tory results, especially in 
localities where insects are 
not too numerous. It 
consists of an iron wire¬ 
holding hook cemented 
into a blown glass bottle, 
which is inverted, so that 
the hook hangs down. 
The bottle is cemented 
into a cast-iron shell, which is either provided with an 
arm that screws into the pole, or, if to be placed on a 
cross-arm, is arranged with a projecting piece, whereby 
it may be inserted into a hole on the under side of the 
cross-arm, and locked by a pin which is passed through 
the cross-arm and engages the projecting piece. 

The remarkable insulating properties of this combina¬ 
tion are due to two causes : first, the liberal use of paraf¬ 
fine, with which the cement is saturated; and, second, 

the great power of repelling moisture possessed by 

blown glass. 

The last insulator which it is necessary to mention is 


It may be well here to state 



Fig. 6G. 





















LINE CONSTRUCTION. 


165 


the “rubber hook.' 5 It is simply an iron liook whose 
shank is firmly fixed into a mass of hard rubber. A 
thread is cut on the rubber for screwing into cross-arms. 
On account of its great mechanical strength and con¬ 
venient form it is much used on short city lines. Its 
high price and the deterioration of its insulating quali¬ 
ties after a few years have prevented its extended use on 
long lines. 

151. What is usually the material of the conductor in aerial 
lines i 

The material of which aerial conductors are made is 
now almost universally iron. The best wire is made of 
•charcoal iron, which, after being drawn, possesses a 
high degree of toughness. Line-wire should invaria¬ 
bly be galvanized. Iron is selected as the best conduc¬ 
tor because it is cheap, durable, has a reasonably low 
resistance to the passage of electricity, and has great 
tensile strength. Copper, on the other hand, cannot be 
ordinarily used, because it has only one of the above 
qualifications in a superior degree to iron—that is, low 
resistance. In that it is much superior, a wire of cop¬ 
per conducting as well as a wire of iron six times its 
cross-section. For this reason it is exclusively used in 
submarine cables. Its disadvantages for land lines are its 
intrinsic value, which renders it at all times liable to 
be cut down and stolen, its inferior tensile strength, 
and its extreme sensitiveness to changes of temperature. 
It has been often tried, but always given up. Com¬ 
pound wire has sometimes been used and has had some 
degree of success. It has a steel core with a copper 
sheathing, so as to combine strength with conductivity. 

Thin steel wires are more or less coming into use for 
short telephone lines, where a high degree of conduc¬ 
tivity is not necessary ; and their advantages are that 
considerable strength is thereby acquired, that much 
lighter fixtures may be used, and that householders are 
much more willing to allow a light wire than a heavy 
one to be attached to their houses. 


166 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


152. What sizes and brands of wire are chiefly employed f 

For telegraph lines of medium length—for example, 

100 to 300 miles—wire of No. 8 or 9 Birmingham gauge 
is generally employed. The size of No. 8 is .165 of an 
inch, its weight tier mile about 385 pounds, and its re¬ 
sistance nearly 13 ohms per mile ; while 409 feet mea¬ 
sure 1 ohm in resistance. The size of No. 9 is about .148 
of an inch, its weight per mile about 324 pounds, its re¬ 
sistance per mile 16.1 ohms, and 328 feet of it give a 
resistance of 1 ohm. 

For very long lines—for example, from New \ork to 
St. Louis or Chicago—Nos. 4 and 6 are used. The size 
of No. 4 is .238 of an inch, and of No. 6 .203 of an inch. 
The weight of No 4 is about 887 pounds to the mile, 
and of No. 6 about 570 pounds. The resistance per 
mile of No. 4 is about ohms, that of No. 6 about 
8J- ohms. For lines but a few miles long—in short, for 
any line less than 25 miles in length—Nos. 10 and 11 
will answer very well, while for very short city lines, 
employed either as telegraph or telephone wires, Nos. 12 
and 14 are as large as necessary. Their sizes and re¬ 
sistances vary as follows : The size of No. 10 in mils, or 
thousandths of an inch, is 134, No. 11 is 120, No. 12 is 
109, and No. 14 is 83. Their respective weights per 
mile are 249, 200, 165, and 95 pounds, and their respec¬ 
tive resistances 19J-, 24J, 29£, and 51 ohms per mile. 
These figures are approximately correct. They are nec¬ 
essarily modified, however, in each individual case by 
the different gauges in use by different manufacturers. 

The best brand of wire for telegraphic purposes is un¬ 
doubtedly charcoal wire. It is now more used in France 
than anywhere else. “ Extra-Best-Best,” known com¬ 
mercially by the cabalistic symbols E. B. B., is gene¬ 
rally used in this country, and is a first-class quality 
of wire. 

153. Have any steps been taken toward the general introduc¬ 
tion of an improved wire-gauge i If so, with what result f 

It lias been universally admitted that the necessity for 


LINE CONSTRUCTION. 


167 


a new and standard wire-gauge is urgent, on account of 
the uncertainty and unreliability of the various gauges 
now in use. The Birmingham gauge has been nomi¬ 
nally the standard by which wire has generally been 
sold, but it lias been ascertained that this gauge varies 
with nearly every manufacturer, so that if wire is or¬ 
dered of a certain gauge there is no certainty that the 
wire received will be of the size required. Moreover, 
the several sizes bear no regular relation to each other. 
For tiiese reasons the necessity for a standard has of 
late been generally acknowledged. Preece & Sive- 
wriglit, in their text-book on telegraphy, recommend a 
gauge based upon weight, giving many good reasons why 
such a standard should be introduced. This gauge was 
proposed by Messrs. Mallock & Preece. It is, however, 
obvious that it is only adapted to one material, since, 
for example, a wire of copper a mile long, with a dia¬ 
meter of 120 mils,* would weigh about 230 pounds, 
while an iron wire of the same diameter would weigh 
200 pounds. In view of the increasing necessity for a 
standard, in 1879 a committee of the Society of Tele¬ 
graph Engineers was appointed to consider the various 
wire-gauges in use and proposed, and to report the most 
proper, if any, for general adoption. In the course of the 
committee’s investigations it was found that no less than 
fourteen gauges were in more or less general use, nine of 
which have the differences in the respective sizes formed 
arbitrarily or by no regular gradation. The other five are 
graded upon the principle of geometrical progression, 
and hence are called geometrical gauges. The commit¬ 
tee, after a careful consideration of each of the fourteen 
gauges, recommended the gauge of Mr. Latimer Clark 
for adoption as a standard. 

This is a geometrical gauge, in which the gradations 
are so arranged that each size is twenty per cent, less 
in weight and electric conductivity than the one imme¬ 
diately preceding it. It varies considerably in many of 

* A mil is a term signifying the thousandth part of an inch. 


168 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

the sizes from the old Birmingham gauge, but is nearer 
to it than any other of the geometrical gauges. 

Notwithstanding the recommendation of this com¬ 
mittee and the necessity of a standard, it does not yet 
appear that the manufacturers have taken the matter 
up practically, and the Birmingham wire-gauge in all 
its delightful uncertainty is still, in this country at all 
events, considered as the wire-gauge. 

154. Should a large or small size gauge of wire he preferred 
for long lines i 

The longer a line the larger should be the gauge of 
wire used, as illustrated by the fact that on the short 
private lines so well known in cities Nos. 11, 12, and 14 
are generally used; on telegraphs of ordinary length 
between commercial points Nos. 8 and 9 are commonly 
employed, and for the longest telegraph lines—such as 
those between New York and Chicago, and New York 
and St. Louis—Nos. 6 and 4 either are or should be 
used. The largest size used in England is No. 4, which 
is nearly a quarter of an inch in diamerter. 

155. What are the reasons for using large tv ires for long 
lines i 

In the first place, the smaller the wire the more care is 
needed in insulation ; the smaller a line-wire is the less 
is its conducting power, and, necessarily, the greater is 
its resistance. In a line the current from a battery has a 
choice of routes, so to speak—either to traverse the line- 
wire, thereby arriving at the distant point, or to leak to 
ground over each insulator and down each pole. A cer¬ 
tain amount of leakage does take place at every pole, 
and therefore the current does actually divide between 
the two routes in direct proportion to their respec¬ 
tive conductivities. Although the amount of electricity 
which leaks off at one pole is inconsiderable, yet when 
we remember that there is an average of thirty poles to 
the mile, and possibly a great number of miles to the 
line, we see that the total amount of leakage is b}^ no 
means inconsiderable. We must further consider that 


LINE CONSTRUCTION. 


169 


the resistance of a line-wire increases in direct propor¬ 
tion to its lengtli; that is, if a wire 100 miles long lias 
a resistance of 1,000 olims, when extended to 200 miles 
long the resistance will be 2,000 ohms, provided the wire 
is kept the same size. The result is that every line, as it 
is made longer, decreases the resistance of its insulation 
by adding many more poles, at each of which there will 
be some leakage, while it also has the resistance of its 
proper conductor increased, because each mile of wire 
adds a mile of resistance. It is obvious, then, that to 
maintain the conductivity of the line at its proper stan¬ 
dard we must increase its size and thereby keep its re¬ 
sistance down. We shall, by so doing, economize bat¬ 
tery power, because reducing the line resistance practi¬ 
cally shortens the circuit. By using smaller batteries 
we gain incidentally another advantage—namely, the de¬ 
creased tension of the current, and consequently its de¬ 
creased ability to escape, or the greater ease with which 
it may be insulated. Another point in favor of large 
wires is that they are much more durable in proportion 
than small ones. 

156 . What sizes and qualities of wire are suitable for tele- 
phone lines t 

Any kind of wire that is suitable for telegraph lines is, 
in the abstract, equally suitable for telephone lines, both 
as a matter of economy in first cost and for ease in man¬ 
ipulation ; it has, however, been found expedient ordi¬ 
narily not to use a larger wire than No. 12, galvanized 
iron. For long lines, such as those between cities, Nos. 
8 and 9 are generally used. 

A much smaller wire of steel can, however, be profita¬ 
bly used on short lines, for the following reasons: A 
small steel wire is as strong as a much larger iron wire. 
It is, therefore, very easy to handle while it is being 
strung, and this is quite a consideration. It is also a 
comparatively easy matter to obtain permission to erect 
a fixture on a roof where very light wires are employed, 
and, moreover, by using small wires induction is much 


170 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

diminished. On the other hand, the resistance of the 
conductor is greatly increased, both because that con¬ 
ductor is steel and because a small wire is used. In¬ 
sulation is thereby rendered proportionately difficult. 
These considerations cannot, however, outweigh the 
previous ones, because on such short lines as those we 
are speaking of—for example, from half a mile to a mile 
long—the resistance, at the greatest, is not so much as 
to render the line at all difficult of insulation ; and, in 
the second place, no sensible difference is perceived in 
using a telephone, even where the resistance is consider¬ 
ably increased. Furthermore, so far as signalling is con¬ 
cerned, the recent practice is decidedly to use magneto- 
electricity for signalling, and such currents can never 
have any difficulty in doing a reasonable amount of 
work or in ringing a bell loudly over more miles of steel 
wire than can be required within the limits of any Ame¬ 
rican city. 

Copper wire has been spoken of," and is used to some 
extent, but its high intrinsic value and the increased 
number of supports rendered necessary by its use will 
prevent its general introduction. Light phosphor-bronze 
wires are used considerably on the Continent of Europe, 
and for some purposes in the United States, especially 
for long spans where a light wire is useful. Its electri¬ 
cal resistance is higher than might have been expected. 

157 . What is meant by the term galvanized wire f 

When we speak of galvanized wire we mean nothing 
more nor less than zinc-coated wire ; and the term gal¬ 
vanization is entirely misapplied when so used. 

Telegraph wire is nearly always galvanized, in order 
to preserve it from destruction by the oxygen of the air. 
If not so protected the wire is eaten away by rust very 
rapidly. When properly applied the zinc coating is 
very effectual in preserving the iron wire from oxida¬ 
tion, and this it accomplishes in two ways : first, by 
acting as a mechanical covering and protection for the 
iron wire ; second, by its electrical qualities being more 


LINE CONSTRUCTION. 


171 


electro positive than iron—that is, having a greater af¬ 
finity for oxygen than iron. When associated with it 
the iron is protected from the action of the oxygen at 
the expense of the zinc. But when the zinc is attacked 
by the atmospheric oxygen it is converted into oxide of 
zinc. This, not being soluble in water, remains on the 
wire, and so protects it from corrosion. In the vicinity 
of places where much coal is burned, however, the air is 
heavily charged with sulphurous acid gas ; this trans¬ 
forms the oxide of zinc into sulphate of zinc, which, 
being readily soluble in water, is washed away, leaving 
the iron unprotected. This is the reason that iron wire 
in the vicinity of large manufacturing towns so soon 
rusts away. If it can be done it is a very good plan to 
paint wires in such localities. Galvanizing is now per¬ 
formed in a much more effective and efficient manner 
than formerly, and, as the wire is by the same process 
annealed, its mechanical qualities are left comparatively 
unimpaired ; still, the iron is by the process made a 
little harder. 

158 . What, mechanical tests are usually applied to telegraph¬ 
ic ire % 

Only two tests are generally applied in America to 
line-wire—namely, for ductility and tensile strength. 
The first is made by twisting short pieces of wire be¬ 
tween two vises ; the second by the direct application 
of weight. Two other tests are desirable and easily ap¬ 
plied. As the value of these tests depends mainly upon 
the way they are applied, we will describe the four 
methods somewhat in detail. 

The first mechanical test which should be applied is 
so simple as to be within the means of every one, and is 
for pitability . The wire should be capable of being bent 
four times to a right angle with itself, while held in 
a vise, without injury. The second test is to the same 
end and is equally easy of application. The wire should 
be capable of being wound around itself a certain num¬ 
ber of times without breaking. The third test is uni- 


172 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

versally employed, both by the Western Union Com¬ 
pany in this country and by the telegraph departments 
in the principal European countries, and, as previously 
indicated, if well performed this test is valuable ; if per¬ 
formed in a slovenly manner it counts for nothing. It is 
to subject a sample of the given wire to twisting, and also 
is a test for ductility. The piece of wire is placed be¬ 
tween two vises six inches apart, and twisted ; the great¬ 
er the number of twists that it will bear without splitting 
or breaking, the better is the ductility of the wire. The 
twists are reckoned by the spiral formed by a line drawn 
longitudinally along the wire with ink before the test. 
The number of the twists in wire of the same quality 
depends upon the size of the wire. For No. 9 it should 
not fall below fifteen twists in the six inches, or for No. 
12 below seventeen. To give the test a proper degree of 
value the vise-jaws should not have sharp edges, or they 
will cut the wire and cause it to break close to the vise. 
The number of twists that any wire should bear varies 
(roughly) inversely with its diameter. That is, the num¬ 
ber of twists that a wire will stand increases in the same 
proportion as its diameter decreases. The fourth test 
is for tensile strength. The wire is required to carry a 
certain weight or resist a certain strain without break¬ 
ing. This test is universal in its application. The re¬ 
quirement of the Western Union Company is that the 
wire must be capable of elongating fifteen per cent, 
without breaking, and that it must not break under a 
less strain than two and a half times its own weight per 
mile. This test is sometimes made with a hydraulic ma- 
•chine, but oftener with a scale and weights. The last 
method is much to be preferred, because in the former 
the additional strain is apt to be too rapidly applied, and 
the wire, not having time to stretch to the individual 
strain, will show a greater strength than it has. Using a 
scale or lever, file weights should be slowly applied and 
the wire given time to stretch. If the wire to be tested 
is to be suspended from a hook, it will not do to fasten 


LINE CONSTRUCTION. 


173 


it with a twist splice, as such a splice will not stand the 
strain. The wire should be closely wound around the 
hook and the end brought down parallel to the wire, the 
two being then closely wrapped with binding-wire. 

159. ITT mt amount of stretching should good iron wire hear 
without breaking 1 

In different countries different standards are given. 
For example, on the government telegraphs in England 
line-wire is required to be able to elongate eighteen per 
cent, before breaking. The Western Union Telegraph 
Company specifies that line-wire must be capable of a fif¬ 
teen per cent, elongation. It is safe to say that any wire 
for telegraphic purposes should at least be capable of 
stretching to the latter percentage. The breaking strain 
should be not less than two and a half times the weight 
of the wire per mile ; that is, if a mile of wire weighs 
two hundred pounds, and a piece of it is undergoing a 
test for strength by suspending weights from it, the wire 
should not break until the amount of weight reaches 
five hundred pounds. 

160. What electrical tests should telegraph-wire he required 
to pass i 

Electrical tests are more especially necessary when the 
wire is to be used on long circuits. The electrical pro¬ 
perties of wire have been found to vary considerably, 
and frequently the strongest and most ductile wire, or 
that which tested mechanically is the best, when electric¬ 
ally tested is found to be much inferior for telegraphic 
purposes to other wires by no means so good otherwise. 

The only test much used, however, is for resistance. 
The ordinary practice in this country is, when ordering 
wire, to stipulate that the resistance of the wire in ohms 
per mile, at 60 degrees Fahr., must not exceed the quo¬ 
tient of the number 5,500 divided by the weight of the 
wire in pounds per mile. For example, if we order No. 
12 wire and assume the weight to be 165 pounds per 
mile, to find out what resistance we require we divide 
5,500 by 165. Finding the quotient to be 33^, we order 




174 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

No. 12 wire, 165 pounds to the mile and with a resist¬ 
ance not higher than 33J ohms per mile. Similarly, a 
wire No. 9—which we will call 325 pounds per mile— 
should have a resistance not greater than 5,500 divided 
by 325, viz., 16f§ ohms. 

161. Does the resistance of wire vary with the temperature t 

Yes ; the resistance of all wires increases as the tem¬ 
perature rises, and the resistance of nearly all metals 
increases at the same rate, iron and thallium, according 
to Dr. Mattliiesen, being the only exceptions. From the 
tables given by Latimer Clark we learn that the resist¬ 
ance of iron wire increases about thirty-five hundredths 
(.35) per cent, for each degree Fahrenheit, and that the 
resistance of copper increases, as the temperature rises, 
twenty-one hundredths (.21) per cent, for each degree. 

The rate of increase is not reckoned all through on the 
original resistance, but is computed in the same manner 
as compound interest on a sum of money. For example, 
if we have a wire which measures 100 ohms at 60 de¬ 
grees Fahrenheit, and the resistance be increased a cer¬ 
tain amount by a rise of one degree in temperature, it 
will be increased by the next degree of rise at the same 
rate per cent., calculated on the original resistance, plus 
the amount increased by the first degree of rise. 

162. The diameter of any iron wire being given , how may 
the 'weight per mile be ascertained l 

If we know the diameter of any size of iron wire, in 

•/ 

mils, or thousandths of an inch, we may find the weight 
per mile by dividing the square of the diameter in mils 
by the constant number 72.15. 

For example, we have a No. 12 iron wire, and wish to 
find its weight per mile. It is, we will suppose, 109 
mils in diameter. The square of 109, or 109 multiplied 
by itself, is 11,881. Dividing this number, 11,881, by 
72.15, we find the quotient to be about 164f pounds, 
which is the weight per mile. The weight of copper 
wire is found in the same way, substituting 63.13 for the 
number 72.15. 


LINE CONSTRUCTION. 


175 


163. What is meant by the killing of wire ? 

It is a term mucli used in England, where it is applied 
to the process of stretching the line-wire in a cold state 
before stringing it. The average amount of length 
gained by thus stretching should be two inches in every 
hundred. The purpose of the operation is not to in¬ 
crease the length of the wire, but it is that weak places, 
caused by bad joints, bad welds, or other imperfections, 
may be detected and the wire broken before it is strung; 
avoiding thus the annoyance of subsequent breakage 
and the trouble and delay attending the necessary re¬ 
pairs. Not only are these weak traces detected by this 
process, but the small bends and wrinkles existing in 
ordinary wire are straightened out, the wire is rendered 
less springy, more manageable, and has much less ten¬ 
dency to cross with other wires when acted on by the 
wind. The method of killing is by Mr. Culley described 
in the following words: “ The wire should be laid out 
at the feet of the poles, drawn as tight as possible by 
ropes and blocks, and then pulled at the centre of its 
length, at a right angle, till it stretches. It will be 
found to have lost its spring and to lie on the ground as 
if it had been killed .” 

164. What is to be understood when the dip of a line-wire 
is spoken off 

The dip of any telegraph line-wire is the sag between 
the poles ; that is, when a wire is strung it is never 
pulled up perfectly tight between the poles, because if 
it were so strung it would break very easily from any 
cause. Consequently, between the poles the wire dips, 
or sags, down in a wide curve, which is deepest at the 
middle of the distance from pole to pole. 

165. How is the tension . or degree of tightness , with which 
wires are strung regulated 1 And is there any dip which is 
regarded as a standard i 

In America there lias been very little regular practice of 
this kind, and the only rule has been for every line fore¬ 
man to do that which was right in his own eyes ; and, in 


176 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

view of such a fact, the small amount of trouble that our 
lines give on the average is astonishing. It is, how¬ 
ever, an obvious fact that line-wires must be strung suffi¬ 
ciently tight to prevent crosses, and sufficiently slack to 
avoid breakage from slight causes or from any ordi¬ 
nary change in the temperature of the air. It has been 
ascertained by the British telegraph engineers that this 
happy medium is attained when the dip, with a tempera¬ 
ture of 60 degrees Fahrenheit, is twenty-four inches in a 
span of one hundred yards. This dip may, then, be ap¬ 
proximately taken as a standard. 

166. When the distance between the poles varies , by what rule 
can the proper dip be ascertained , in order to maintain the 
wire at the same distance from the ground at the loicest point 
of each span t 

The dip of any span of wire—that is, the actual per¬ 
pendicular distance from the highest point of the span 
to the lowest—varies, not in proportion to tlie^ distance 
between one pole and the next, but with the square of 
that distance. 

It adds much to the symmetrical appearance of a line, 
to say nothing of its superior operation, when the ten¬ 
sion is made uniform from pole to all through the 
line ; and this may be secured by remembering the state¬ 
ment given in the previous answer. We have already 
seen that 24 inches in a hundred yards may be taken as 
a standard, and we now see from the foregoing observa¬ 
tions that the formula for finding any required dip must 
be : That the square of 100 bears the same proportion to 
the square of the length of the span under consideration 
as 24 does to the dip required in inches. If, then, we wish 
from this to ascertain the height of the supports on the 
poles, so as to keep the dip between the spans a uniform 
distance from the ground, all that we have to do is to 
add the amount of dip, which we have ascertained, to 
the distance which Ave have decided upon as the distance 
from the loAA r est point of each span to the ground, which 
gives as a result the height of pole support required. 


LINE CONSTRUCTION. 


177 


To reduce these rules to practice we illustrate by the 
following examples: We have a line, and the majority 
of the poles are 100 yards apart. Some spans, however, 
are, from circumstances over which we have no control, 
150 yards long, and one 200 yards long. It is required 
to find the proper dip that should be allowed in the 
longer spans, so as to keep the wire at an even distance 
of 25 feet from the ground at the lowest point of each span. 

We do this as follows, keeping in mind the above for¬ 
mula : Finding that the square of 100 is 10,000, and that 
the square of 150 is 22,500, by simple proportion it is 
readily ascertained that 10,000 is to 22,500 as 24 is to 54 
inches, or 4 feet and 6 inches. This, therefore, is the 
requisite dip for a span 150 yards long. Now, to find 
the height at which this span should be supported at 
the poles, all we need do is to add the 25 feet that we 
have stipulated for as the lowest point of the dip to 
the dip itself—25 feet added to 4 feet 6 inches gives a 
height of 29 feet 6 inches, which must be the height of 
the insulator from the ground. 

We now consider the span of 200 feet long, and pro¬ 
ceed as before. The square of 100, that is, 10,000, bears 
the same proportion to the square of 200, or 40,000, as 
24 bears to 96 inches, or 8 feet. Eight feet, therefore, 
must be allowed in this case, and the supports made 33 
feet from the ground. In these remarks it is not to be 
understood that an arbitrary standard of 24 inches dip in 
100 yards is insisted upon ; but having already decided 
upon a standard dip, it is desired to show how to main¬ 
tain that dip uniform. 

167. What are the different styles of line-wire joint or splice 
in general use f How are they made , and which is the best f 

The joint in general use in America is the common 
twist-joint. The Britannia joint is always used in En¬ 
gland, and a peculiar joint, in which both wire ends are 
twisted together round each other, is used in France. A 
joint which should never, under any circumstances, be 
used anywhere is the so-called bell-hanger’s joint. 


178 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


In describing how they are made we will take the last 
lirst. The bell-hanger's joint is made by simply hook¬ 
ing the two wires together and bending back the ends. 
No telegraph man using this, even as a makeshift, can 
hope for success in his business. 

The French joint is made by laying the ends to be 
spliced together for about six inches ; a particular form 
of hand-vise is then screwed to each end, and the two 
vises turned in opposite directions until the ends are 
completely wound on. 

The Britannia joint is much praised by English wri¬ 
ters, and, from its construction, must necessarily be an 
excellent joint. It is made by bending the extreme 
ends of the wires short up with the pliers, placing the 
wires side by side, and then binding No. 1G wire tightly 
around them. The whole is tlien well soldered. Of 
course, before making the joint the ends are "made per¬ 
fectly clean and bright. 

The American twist-joint is shown in Figure 67, and, 
though not a masterpiece of electrical engineering, will 



always maintain its popularity on account of the ease 
and rapidity with which it is made. In making this 
joint, after cleaning the ends until a bright metallic sur¬ 
face is obtained, the ends are put together and each one 
in turn twisted round the other, making the successive 
turns as close to each other and as nearly at right angles 
to the line as possible. Make four or five turns, then 
cut off the ends close to the splice. In the construction 
of a line nothing is more essential to its success than the 
perfection of its joints. Nothing like the attention that 
the subject deserves has been given to it in this country. 

Evexy joint should be soldered, whether between iron 
and iron or between iron and copper. A single defec- 









LINE CONSTRUCTION. 


179 


five joint will often exceed fifty miles of line in resist¬ 
ance. A case once fell within the writer’s own experi¬ 
ence where a short local line, whose normal resistance 
was less than 250 ohms, rose to 2,500 ohms. This resist¬ 
ance was located and found to be all in one point, be¬ 
tween an iron and a copper wire; the joint was unsol¬ 
dered. 

When a chloride of-zinc solution is used for soldering 
copper and iron, before leaving the joint it should be 
washed off. It is better, however, in such a case to use 
resin as a flux. 

168. What is the cause of the humming noise often heard 
xchere wires are attached , and how may it be prevented f 

This noise, which is frequently so loud as to be very 
annoying, especially to the inmates of houses over which 
the wires are run, is caused by the vibration of the wires 
under the influence of the wind, in the manner of an 
iEolian harp. It may be prevented in the following 
way : Two pieces of stout india-rubber tube, like that 
used for covering the rollers of wringing-machines, are 
cut about two inches long, and one is fastened at each 
end of a piece of line-wire, four or five feet long, by 
passing the wire through it and twisting it back on 
itself. This piece of wire is then fastened at its centre 
to the insulator, as usual, by a tie-wire. The line-wire 
is then cut and an end fastened to each of the sections 
of hose by passing it round the outside of the piece of 
hose, and twisting. To preserve the continuity of the 
line a small iron or copper wire is then connected and 
soldered to the two ends of the line beyond the rubber. 
The insertion of a piece of small-sized metallic chain in 
the line, provided with a continuity-preserving small 
wire, is also sometimes successfully adopted. Other 
remedies, all tending to the same end, are occasionally 
employed, the main object in each case being to prevent 
the vibration by interposing a damper. 

169. How should an aerial line be led into a way-station ? 

There are several methods. In an ordinary telegraph 


180 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

line the usual way is to plant a pole directly in front of 
the window into which the wires are to enter, and run 
the wires from each side to a separate bracket and in¬ 
sulator, from thence looping them in. For short lines, 
such as those in cities, which are frequently house-top 
wires, a mode often adopted is to run the wire to a 
batten or counter-brace overhanging the eave, fasten it 
there to a hook insulator, and then drop it down to a 
block of wood, bevelled on one corner, which is spiked 
to the wall close to the window where an entrance is to 
be made. Another way is to divide the line by the in¬ 
sertion of a non-conducting substance, such as a block 
or ring of glass or rubber, and to attach the conducting 
wire to the main wire on both sides of the insulator. To 
conduct the wires from the point where the line-wire 
terminates there are also various plans in use. If the 
line is not a new one, but is already in use, a cut out 
must invariably be applied across the new loop until the 
job is complete ; that is, the two wires of the loop must 
be connected by a short wire. The ordinary line-wire 
may be led into an office if a hard-rubber tube is insert¬ 
ed into the entering hole. The tube is fastened in the 
hole with its outer end inclined down, so that no mois¬ 
ture can enter, and the wires then passed through and 
fastened on the inside. Another way often used is to 
terminate the line-wire at the hook, or insulator, just 
outside the entering hole, by twisting it around the 
hook and then wrapping it back on itself. About four 
inches of the line-wire outside of the twist-joint are then 
brightened, and a piece of kerite or rubber-covered wire 
stripped at the end for about eight inches; the bared 
wire is also made very bright, and is then, commencing 
at the lowest point, carefully and tightly wound around 
the brightened part of the line-wire. The covered wire 
is finally led through the hole in the window or wall and 
secured in any desirable way on the inside.* 

* It is well to know that gutta-percha-coverecl wire is not suitable for 
this kind of work unless well covered with tape soaked in preserving mix- 


LINE CONSTRUCTION. 


181 


Sometimes, when many wires enter a building, a cu¬ 
pola is built for their reception. On entering they are 
led to binding-posts, from whence they are directed to 
any desirable point. 

This work of leading in wires is very important, as, if 
unskilfully or negligently performed, escapes are very 
likely to occur in or about the window-casing. 

170. How should an aerial line he led into a terminal office f 

Where many lines—either pole or house-top—are run, 

a cupola is frequently used, into which the wires are led, 
as indicated above. 

Sometimes also they are terminated at a pole by wind¬ 
ing them back on themselves after being bound to the 
insulator. A plan often adopted in cities is to range 
a cross bar outside the window where the wires are to 
enter, and screw a sufficient number of hook insulators 
into it, upon which the wires coming down from the fix¬ 
ture or pole are terminated by winding back. 

171. Are aerial wires ever carried in cables % 

Yes; it is often desirable to run a number of wires over 
the same route for a short distance where the available 
space is circumscribed. In such cases cables are very 
useful, and are employed by several of the city tele¬ 
phone companies of America. 

They will be still more universally employed in the 
future, as the number of wires is, owing to the rapid ex¬ 
tension of telephonic communication, daily increasing. 

The idea of suspending light cables, containing a num¬ 
ber of wires, in the air and over the house-tops, is due to 
Sir Charles Wheatstone, who suggested it some eighteen 
years ago. Cables containing as many as fifty wires 
have been in use in London for a long time, and are sus¬ 
pended by frequent hooks from No. 8 wires. Some of 
the principal telephone exchanges of the United States 
have extensively adopted the use of the aerial cable and 
find it to be a great convenience. San Francisco and 

ture consisting of wood-tar, gas-tar, and slacked lime, because the gutta¬ 
percha is soon oxidized and rendered useless by the action of the air. 


182 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

Pittsburgh were among the first cities to use such cables, 
but many are now to be found in Boston, New York, 
Cincinnati, and other places. 

172. Describe the construction of the cables most frequently 
used in telephone work. 

One of the cables, which is said to give excellent ser¬ 
vice, is that made by the Western Electric Company, 
and consists of a number of cotton-covered copper wires 
enclosed in a leaden tube and surrounded by peculiarly 
prepared paraffine. Two No. 8 wires are affixed to the 
lead pipe in a long spiral, and bound to it by a small 
iron wire, the two sizes of wire being soldered to one an¬ 
other and also to the pipe for the purpose of facilitating 
suspension. 

A second variety, much used, is' the kerite cable of 
Day. The required number of copper conductors are 
first separately insulated with kerite ; each insulated 
conductor is also surrounded by tinfoil ; tlie tinfoil of 
all the conductors thus forms one continuous surface, 
which, at the two ends of the cable and at any other 
necessary point, is united to ground-wires to carry off 
interfering currents. Over all is wound a strong enve¬ 
lope of kerite tape. 

A third cable is that made by E. F. Phillips, of Provi¬ 
dence, R. I. It can be made to contain any number of 
conductors, and a hundred-wire cable has a diameter of 
only an inch and a quarter. As usually made the con¬ 
ductors are of No. 20 copper wire, each covered with 
rubber. Over the rubber, as in the kerite cables, is 
lapped a metallic surface to be connected with the earth. 
An envelope of rubber is placed outside of this, and 
over all a covering of stout hose is woven, and this, 
when well tarred or painted, completes the construction 
of the cable. 

All of these cables have a very high standard of in¬ 
sulation, and each variety has given satisfaction where 
employed. In suspending such cables lightning-arrest¬ 
ers must be carefully applied at each end, and, if the 


LINE CONSTKUCTION. 


183 


cable is long, it will do no harm to attach a third in the 
middle, the cable being divided and the conductors 
fanned or spread out for the purpose. 

173. Are covered wires ever used on liouse-top lines t 

Yes; in cities, particularly between the centres of 
business, it becomes almost a necessity to employ 
covered wires, on account of the great number of lines 
which cross and recross each other in every direction. 
In Yew York, for example, the Gold and Stock Tele¬ 
graph Company uses rubber-covered or kerite line-wire ; 
and many troubles of a minor character to which its 
lines would otherwise be peculiarly liable, by reason 
of the high tension currents employed on printing cir¬ 
cuits, are thus prevented or rendered innocuous.* 

* It may be well to mention that telephone lines can be worked to a con¬ 
siderable extent without insulators, tests having been made on lines in 
southern Indiana which indicate that perfect insulation on such lines is by 
no means essential. It is claimed by persons who have made tests that the 
absence of insulators, or, in other words, an imperfect earth-contact on the 
line, operates as a preventive of inductive interference between lines. It is, 
moreover, well known that articulate conversation may be carried on over 
short lines which wholly or in part lie on the ground. 


CHAPTER XIII. 


SUBTERRANEAN AND SUBMARINE CONDUCTORS. 

174. What metal is usually preferred for the conducting-wires 
in underground work, and what materials are chiefly used in 
insulation ? 

Copper lias always been used as an underground tele¬ 
graph wire, to the exclusion of all other materials ; the 
most usual size is No. 18, covered with gutta-percha 
till it reaches the size of No. 7, 13. W. G. In England 
these wires are wrapped with strong cotton tape satu¬ 
rated with Stockholm tar, and drawn into buried leaden 
or iron tubes. At suitable distances apart are laid test¬ 
ing and drawing-in boxes, into which the ends of the 
tubes project ; and by means of these boxes or chambers 
access may at any time be had to the wires, and all neces¬ 
sary repairs or changes made. Insulating materials of 
almost every description have been tried. Gutta-perclia 
and india-rubber are, however, the principal materials 
used at the present day. The latter has, upon the whole, 
given the best results when it has been protected from 
air and insects. Kerite* has given satisfaction, and is 
much used in the United States. 

175. When icas the first underground telegraph laid , and by 
whom t 

The first underground telegraph line ever laid was 
that of Francis Ronalds, an English gentleman, in the 
year 1816. He invented a telegraph to be operated by 
synchronously moving dials in conjunction with static 
electricity, and worked it over a wire live hundred and 

* Kerite is a compound of oxidized vegetable oils with tar or asphal- 
tum, which is applied to the wire and afterwards vulcanized by sulphur 
and heat. Patented by Austin G. Day, October 9, 18G6. 

184 * 


SUBTERRANEAN AND SUBMARINE CONDUCTORS. 185 

twenty-five feet long, which was laid in a trench dug 
in the eartli for that purpose. The wire was placed in 
tubes of thick glass, and these were laid in troughs of 
dry wood, two inches square, filled in with pitch. Ron¬ 
alds was a strenuous advocate, at that early day, of un¬ 
derground telegraphs. 

176. Are underground wires at present laid to any great ex¬ 
tent , and where f 

Underground lines are extensively employed in some 
of the cities of England, and, as constructed, appear to 
work well. Several longer lines are also in use, notably 
one between Liverpool and Manchester, a distance of 
about thirty-six miles. More than one hundred miles 
of piping are laid down in England, containing over three 
thousand miles of wire. In Germany, also, there is an 
extensive underground system, which, instead of con¬ 
sisting, like the English lines, of a large number of wires 
laid in pipes, resembles a submarine telegraph : a num¬ 
ber of wires are formed into a cable, which is served 
with tarred rope and armored with galvanized wire, after 
which it is laid in a trench under the public roads or 
highways, and the trench filled up with bitumen. Many 
miles of cable are so laid, and the German government 
officials have been so well pleased with the operation 
of this system that they have lately considerably ex¬ 
tended it. Underground telegraph-wires, however, can¬ 
not be worked at the speed that aerial lines are capa¬ 
ble of, on account of the static induction existing be¬ 
tween them and the earth, which is greatly increased by 
their close proximity to the latter, and which tends to 
retard the signalling currents. 

177. Are underground lines suitable for telephonic circuits % 

Underground lines, up to the present time, have not 

been used to any extent for telephonic purposes. There 
are several reasons for this. Among others, it is evi¬ 
dent, from the fact that telephone wires, even when com¬ 
paratively a long distance apart, interfere seriously 
with eacii other by the development of induced cur- 


186 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


rents and other disturbing agencies, that such interfere 
ing influences would be considerably amplified in tlieir 
strength and scope if the conducting-wires were for a 
great distance placed as close to each other as would be 
necessary in an underground system. The near pres¬ 
ence of the earth, moreover, exercises a retarding effect 
on the telephonic currents, causing them to become in¬ 
distinguishable when the length of the underground 
conductor is more than four or five miles. A partial 
remedy for both of these annoyances is to arrange the 
conductors in metallic circuit, especially when the two- 
wires of the circuit are twisted together. Other reme¬ 
dies have been proposed, and have met with more or 
less success. ^ 

The great objection, however, is the enormous ex¬ 
pense contingent on a first class and thoroughly well- 
constructed underground system, especially in a city 
system of short lines which have to be tapped at many 
points. The expense, though, would be nearly all first 
.construction, as, when once properly laid, the wires 
would be secure from the effects of wind and weather. 

A notable exception to the statement commencing this 
section must be made in favor of the telephone-wires of 
Paris. In that city all the circuits have a metallic re¬ 
turn, and are extended upon supports arranged upon 
the walls of the city sewers, which are spacious subter¬ 
ranean vaults. 

It lias been proposed to arrange the telephone-wires 
of American cities in cables—for example, of lengths va¬ 
rying from half a mile to a mile—and run these cables 
underground to a number of central points, such as 
courtyards or areas surrounded by houses, from which 
central points they may readily be extended to the sur¬ 
rounding buildings. 

Since the foregoing was written steps have been taken 
to construct an underground system of telephonic con¬ 
ductors in Boston, Mass. 

This has been undertaken by the American Bell Tele- 


SUBTERRANEAN AND SUBMARINE CONDUCTORS. 187 


phone Company, and tlie construction is upon the fol¬ 
lowing plan : Cables carrying multiple conductors are 
laid in iron tubes, which are embedded in the earth and 
extend in sections between a number of vaults, cellars, 
or working chambers. The several wires are brought 
out from these cellars at various central points, and 
radiate to the different sub-stations which are adjacent 
to such central points. In the prosecution of this design 
a trench is excavated about four feet deep in the middle 
of the street, and is paved with a layer of common 
hydraulic cement five or six inches thick. Upon this 
bed is laid a number of three-inch wrouglit-iron pipes, 
jointed together by sleeve couplings, screwed on by 
means of gas-thread, each of the joints being served 
with red-lead and thus made water-tight. A second 
thick layer of cement is then applied, and upon that a 
second layer of pipes is laid. The cement is then laid 
on and over the upper layer of pipes so as to embed the 
whole of them and cause them to be completely imper¬ 
vious to moisture. At or near each street intersection a 
vault is built of brick, the bottom of which is deeper 
than the lowest point of the trench. The series of pipes 
from either side enter these vaults, and in them the 
wires can be inter-connected, interchanged, and manipu¬ 
lated as may be found desirable. 

Two routes are led from the Central Telephone Office. 

The several vaults, in addition to being carefully and 
massively walled, are further protected from moisture 
by pouring hot pitch between each course of brickwork 
and the surrounding earth. As each pipe is laid a 
strong iron wire is threaded through it, so that when a 
line of pipe is comjffete between any two working vaults 
a continuous wire is also inside that pipe between the 
vaults, and by attaching groups of insulated wires or 
cables to this threaded wire they can be drawn through 
from vault to vault. 

Several varieties and grades of cable are to be experi¬ 
mented with. 


188 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


To bring the different wires out where they are re- 
■quired several plans have been contemplated. 

In some cases it will be most practicable to run lateral 
branches from the vaults into adjoining cellars or court¬ 
yards, and from these run tubing of an ornamental cha¬ 
racter up the side-walls of the surrounding buildings, 
and thus distribute the wires to their several termini. 
Another plan, and one likely to be adopted, is to erect 
a high hollow pole or column near the man-hole of the 
vault, run the wires up through this column, and from 
the top radiate them to their different destinations. 

It is fully recognized that this attempt to lay under¬ 
ground telephone lines is at present purely experi¬ 
mental ; and until the lines are completed and put in 
operation it is impossible to say how they will work, in¬ 
asmuch as the well-known deleterious effects of static 
and dynamic induction may be intensified by the imme¬ 
diate proximity of the wires to one another and to the 
earth, and communication be thus made difficult, if not 
entirely prevented. 

Such of these underground lines as have been com¬ 
pleted and tried show quite perceptibly a sluggishness 
of operation and a slight indistinctness in the reproduc¬ 
tion of articulation, which is evidently due to retarda- 
tion, and which becomes intensified when the lines are 
connected through the Central Office switchboard with a 
longer line. 

O 

178. What is meant by the term retardation f 

Retardation is the technical term given to a cer¬ 
tain sluggishness of action which is observed when elec¬ 
trical currents are sent into long lines, particularly long 
covered wires, such as underground wires or submarine 
cables, because such wires are much nearer the earth 
than overhead lines. It is caused by the inductive ac¬ 
tion which arises between the conductor and the earth. 

We have seen that an electrified body has an influence 
all conducting bodies in its immediate vicinity, caus¬ 
ing them to exhibit signs of electrification. This is a 


SUBTERRANEAN and submarine conductors. 189 


case in point. The current sent into the conducting- 
wire attracts by this induction, through the insulating 
covering, an opposite electricity from the earth ; and this 
opposite electricity, in turn, attracts the current passing 
in the conductor, and tends to hold it where it happens 
to be—in short, to transform it from dynamic or current 
electricity to static or resting electricity. Thus we see 
that the first part of every current sent is, if we may so 
speak, held or detained by the cable to balance the in¬ 
duced opposing electricity of the earth, and it is not 
until the conducting-surface of the wire is charged that 
any current can make its appearance at the distant end. 
Signals are thus delayed, and the delay experienced is 
called retardation. 

As overhead lines are so much further from the earth, 
they 'are much less troubled by electro-static induction 
and its effects, and it has been estimated that in this 
country the charge retained by an overhead line of from 
thirty to fifty miles long is approximately equal to that 
of about one mile of ordinary submarine cable. 

179. How are the conductors in submarine cables ordinarily 
insidcited l 

Only three substances have been found suitable as in¬ 
sulators for submarine cables—gutta-percha, india-rub¬ 
ber, and Hooper’s material, which is india-rubber pecu¬ 
liarly treated. Of these gutta-percha has been and is 
most frequently used, on account of its well-known dura¬ 
bility, being practically indestructible under water. It 
is not so good an insulator as india-rubber, and, inas¬ 
much as it loses considerable of its insulating power by 
heat, it is, in warm climates, to a great extent supersed¬ 
ed by india-rubber, especially that of Hooper. 

At least three layers of the insulating medium are 
always used and are necessary. The insulation of ca¬ 
bles ordinarily improves after they are laid, all things 
being equal. The insulation, per knot, of the Atlantic 
cable of 1866, which is insulated with gutta-percha, is 
340,000,000 ohms; that of the French cable of 1869, 


190 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

from Brest to St. Pierre, insulated also with gutta-per- 
eha. is 235,000,000 ; while the cable laid in the Persian 
Gulf in 1868, and insulated with Hooper’s india-rubber, 
attained the wonderful insulation of 3,900 megohms per 
knot. Even this has since been exceeded by cables of 
later date, insulated with the same material. 

180. What is the general construction of a submarine cable i 

Submarine cables are usually constructed by embed¬ 
ding a certain number of copper conducting wires— 
which may be either single wires or a strand of several 
small wires—in a good insulating material, such as gut¬ 
ta-percha or Hooper’s india-rubber, applied in succes¬ 
sive coatings. This, again, for protection, is surround¬ 
ed with tarred hemp, and an armor, consisting of several 

strands of large iron wire, is wound 
outside of all. These iron wires, in 
several long deep-sea cables, are also 
covered with tarred hemp. The Atlan¬ 
tic cable of 1865, for example, which 
is shown in section in Figure 68, con¬ 
tains a central conductor consisting of 
seven copper wires twisted together. 
This is covered by four layers of gutta-percha, while be¬ 
tween each layer a compound is applied which not only 
aids the insulation, but tends to unite the gutta-percha 
layers with each other. This is known as Chatterton’s 
compound. Its component parts are gutta-percha, resin, 
and wood-tar. This core is then covered with a layer 
of hemp in five strands, well served with a compound 
of Stockholm tar, pitch, linseed-oil, and beeswax. The 
whole is then covered by ten strands of charcoal-iron, 
each strand covered with hemp. Thus the copper wire 
is a conductor, the gutta-percha and Chatterton’s com¬ 
pound being for insulation, and the hemp and iron wire 
for protection. 

181. Can the telephone be operated successfully over long 
submarine cables f 

It is recorded by Du Moncel, in his work on the tele- 



SUBTERRANEAN AND SUBMARINE CONDUCTORS. 191 

plione, that speech lias been perfectly transmitted and 
reproduced between Guernsey, an island in the English 
Channel, and Dartmouth, a town on the coast of Devon¬ 
shire, a distance of sixty miles. W. H. Preece has also 
successfully conversed over the Dublin and Holyhead 
cable, a distance of sixty-seven miles. M. Herz, by his 
improved arrangement of circuits and telephones, is said 
to have conversed easily between a point on the French 
coast and Penzance; and other electricians and experi¬ 
menters have communicated between Calais and Dover 
with more or less success. On the other hand, it must 
be confessed that no such success has been met with on 
this side of the Atlantic ; or, if it has been achieved, it 
has not been recorded ; and we have no trustworthy in¬ 
formation that telephonic conversation has been effected 
over a greater distance than twelve miles of submarine 
cable. And since the greater distances traversed in Eu¬ 
rope by the articulating currents have not been put to 
an extended commercial use, we are inclined to the be¬ 
lief that, although submarine telephony may readily be 
experimentally effected, it is not yet sufficiently practi¬ 
cal to enable it to be regarded as a commercial success. 


CHAPTER XIV. 


OFFICE-WIRES, AND FITTINGS AND INSTRUMENTS. 

182. What wire may be used in fitting up an office , and how 
should it be attached to the walls or ceilings i 

It is too frequently the practice with telegraph em¬ 
ployees in general to use No. 14 covered copper wire, and 
to stretch the wires loosely in and along the ceiling in 
any way so as to get them in ; but it is as easy (and 
much more satisfactory when done) to do a job of wire¬ 
running in a tasteful as in a slovenly manner, although 
it requires great skill and experience to run the inside 
wires of a telegraph or telephone office in a manner both 
useful and ornamental. 

To do this it has been found in practice that it is bet¬ 
ter to use braid-coated copper wire of a gauge not ex¬ 
ceeding No. 18. To have this wire colored often gives a 
very tasteful effect, especially when colored red. But, 
in any case, No. 18 is sufficiently large to serve every 
practical purpose, while it is much easier to handle and 
gives a better general effect when strung. The wires 
when chosen should, if numerous, be strung through 
cleats of black walnut pierced with the required num¬ 
ber of holes, which should only be large enough to let 
the wire pass through easily. If more than fifty wires 
are to be put up it will often be found necessary to bore 
more than one row of holes and run the wire two or 
more tiers deep. Each cleat should be screwed to a 
base-board of hard wood, which is to be screwed to the 
ceiling. This is to give a greater purchase to resist the 
strain of the wires when pulled tight. The wires should 
be secured with a half-hitch to the first cleat, and, when 
passed through all of them, tightened up, so as to take 

192 


OFFICE WIRES, FITTINGS, ETC. 


193 


out all the slack, and anchored by another half hitch at 
the last cleat, which should be about two feet above the 
switch-board, if one is used. Instead of then bringing 
them straight down to the switch it is better to coil 
them into loose spirals, as it adds to the general effect 
and also gives slack if any wire should break. If only 
two wires are to be arranged it is sometimes convenient 
to string them on opposite sides of a row of porcelain 
knobs till they reach the instruments. 

Where extremely powerful currents are used—as, for 
example, those employed by the Gold and Stock Tele¬ 
graph Company—the office-wires need a much more ef¬ 
fectual insulation than paraffined cotton, and kei ite or 
rubber covered is generally employed. In large West¬ 
ern Union offices the wires are usually secreted as much 
as possible. 

Close to the entering point of a building a light¬ 
ning-arrester should always be placed, which should be 
connected to a very efficient ground wire. Every wire 
entering the office ought to pass through the lightning- 
arrester. The lightning-arrester ground should never 
run to a lead pipe or to the same ground that other 
wires are led to. 

A favorite method which has lately been much em¬ 
ployed by telephonic constructors, and which is excel¬ 
lent, is to run the wires clear down to the switch-board 
in twenty-five or fifty wire cables. This gives a very 
clean and neat appearance to the office. It is a very 
good plan also to keep the wires out of sight altogether, 
which may be done by ranging them in troughs along 
the floor and bringing every wire to the switch-board at 
its rear. 

183. How should a ground-wire be constructed in order to in¬ 
sure efficiency i 

Three distinct services are required of the ground-wire 
in practical work—namely, to act as the terminal of 
main lines, to attach to lightning-arresters, and to use 
for testing purposes. 


194 ELECTRICITY, MAGNETISM, AND TELEGRAPHY'. 


In a well-appointed office three separate wires will be 
used, one devoted to each of these purposes, and all run¬ 
ning to earth at different points. 

Too much attention can never be given to this all-im¬ 
portant subject. It is, indeed, the groundwork or basis 
of all telegraph or telephone line-construction, and it 
may be broadly stated that no matter how well a wire 
may be strung, or how perfectly the instruments and 
batteries are connected, if the terminal grounds be im¬ 
perfect the working will also be imperfect. 

No better ground can be secured than the iron water- 


pipe of a town or city, and this should, if possible, 
always be secured. An iron gas-pipe will, however, 
serve a very good purpose, provided the connection be 
made outside of the meter ; this precaution is necessary 
because the meter is sometimes removed, and because 
the joints of gas-pipe are frequently made in red and 
white lead, which substances are non-conductors. In the 
case of water-pipes the water inside aids the pipe in its 
conducting powers. If neither water nor gas pipes can 
be found, a plate of metal, not less than two feet square, 
may be provided, the metal either being tinned or gal¬ 
vanized iron or copper. This should be buried edgewise 
in ground which is always damp, and the ground-wire 
attached to it by riveting and soldering. We have 
known good ground-wires being formed by attaching 
wires to a pipe of a steam-heater, first brightening the 
pipe. If both water and gas pipes are at hand the 
ground wire should be securely attached to both, so 
that if one be cut or broken the other will remain to 
preserve the continuity of the line. Lead gas-pipes 
should never be employed ; they are dangerous. A dis¬ 
charge of lightning has been known to melt a lead gas- 
pipe attached to a ground-wire and to set fire to the 


escaping gas. 

We are aware that it has been common to ridicule the 
idea of insulating the ground-wire; it is nevertheless 
true that a terminal ground should always be insulated. 


OFFICE WIRES, FITTINGS, ETC. 


195 


'This is both to protect it and to keep the battery current 
uniformly at the same strength. If a ground-wire be 
not insulated it is likely to corrode at any point at 
which it may find earth between the main ground and 
the battery. 

To make an excellent connection about six feet of 
bright, bare copper wire should be taken, about No. 
16 or 18 gauge; the gas or water pipe having been filed 
clean for a length of about three inches, the wire should 
be carefully, tightly, and regularly wound round, and as 
the end of the wire approaches it should be interwoven 
among the convolutions and drawn tight; when about 
eight inches is left unwound it should be well spliced 
to the insulated wire leading from the instruments and 
line. 

Both splice and coils should then be soldered. A 
clamp is in some cases used, but it is not to be recom¬ 
mended, as screws generally work loose in some mys¬ 
terious manner. In offices where many wires centre— 
for example, the central office of a telephone system— 
it is desirable that as many independent ground-wires 
should be constructed as can be readily done. 

For lightning-arrester grounds a very large wire 
should be run directly from the lightning-arrester to 
earth, at the nearest convenient point, and connected 
in the way already described. 

Testing grounds may generally be constructed in the 
same manner. It is under this head that the ground- 
wires of a way telegraph-office come. For such an of¬ 
fice it is well enough to use the same wire also as a light¬ 
ning arrester ground. 

It may be remarked that every telegraph engineer 
must have noticed the extreme difficulty of making a 
good earth-connection when wanted, and the perverse fa¬ 
cility with which a ground will come on a line when it is 
not wanted. In short lines care must be taken to have 
the earth-plate or pipe of the same metal at both ends, 
or a current will be set up, arising from the action 


196 ELECTRICITY, MAGNETISM, AND TELEGRAPHY". 


of the damp earth on the two dissimilar metals when 
united by a conductor. It is well to dispense with an 
earth return altogether in extremely short lines, using 
a wire so as to form a metallic circuit. 

184 . What is the best arrangement of instruments in a tele¬ 
graph office operated on the ordinary Morse system f 

In an ordinary way-office the apparatus consists of the 
following instruments : a relay and key in the main-line 
circuit, a sounder or register and local battery in the 
local circuit, and a switch and lightning-arrester ; the 
latter is often combined with the former. 

The switch, or, if there is none, the cut-out, is placed 
on the wall and the office-wires led to it. If it is a 
Western Union pin-switch the leading-in wires are led 
to the binding-posts connected to the upright metallic 
bars, where they remain open until the pins are inserted. 
Two other wires, called the instrument-wires, are led, 
from the side binding-screws, under the table ; and after 
the relay, sounder or register, and key are placed in 
position, holes are bored through the table near to the 
main-line binding posts of the relay (these are usually 
placed at the right-hand end of the relay); the key is 
then fixed in place, holes being bored through the table 
for its legs, and the wire connected. The order of the 
instruments is indifferent; that is, it does not matter 
which comes first or last. One of the main wires is led 
to one leg of the key, and there fastened to it. A short 
wire is run from the other leg of the key to one of the 
relay binding-posts. The other main wire is then con¬ 
nected to the remaining relay binding-screw, and the 
main circuit is complete, the order being as follows : 
line wire, key, relay, line wire. The pegs are now in¬ 
serted in the switch. The local circuit includes the lo¬ 
cal battery, the relay-points, and the sounder, or regis¬ 
ter, and is run as follows : After setting up the local 
battery, which usually consists of two cells, run a wire 
from one pole, say the copper, to one of the binding- 
screws of the sounder, which, like the relay, has holes 


OFFICE WIRES, FITTINGS, ETC. 


197 


bored near it; then another wire from the other sounder- 
screw to one of the local screws of the relay (these are 
usually at the left-hand end of the instrument), and a 
third wire from the other relay local screw to the other 
pole of the battery. It is perhaps almost unnecessary 
to say that these office connections must always be made 
with covered wire, and particular care should be taken 
to keep all screws tight. 

The sounder, or register, is most conveniently placed 
near the centre of the table, and if a register is used 
the paper-reels should be fixed one at each end—one to 
deliver the paper to the register and the other to receive 
the paper as it comes from the register; the relay is pre¬ 
ferably placed at the left of the register, and at the rear 
of the table, while the key is placed at the right, also at 
the rear of the table, so that an operator, when sending, 
has the breadth of the table whereon to rest his arm. A 
terminal station is arranged on the same principle, but, 
as only one wire comes in for each line, the other end 
goes to the main battery and ground. For example, 
the wire entering the office is led to the switch-board, 
thence to the relay, thence to the key, after which it is 
carried to the battery, and the other pole of the battery 
is connected to the ground. 

185 . What is a switch-hoard f 

It is a piece of apparatus adapted for the convenient 
and easy cross-connection or interchange of circuits. It 
is made use of almost universally in telegraph offices 
where there are more than one wire. By its use differ¬ 
ent circuits are connected together, circuits are divided, 
testing operations are carried on, batteries are readily 
connected, disconnected, or changed, and the wires are 
connected to any desired instruments. The varieties of 
switch-boards are very numerous, but they are nearly 
all constructed on essentially the same principle. This 
principle is embodied in the universal switch, which 
is, briefly, a frame or base-board of hard wood or some 
suitable non-conducting material, on which are fixed 


198 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

two sets of metallic conducting strips, bars or wires, 
crossing each other at right angles, but completely in¬ 
sulated from each other, and means for connecting any 
conductor of one set with any conductor of the other. 
The chief difference between the numerous forms of 
switch-board is in the methods adopted of making such 
connection. 

The most familiar switch-board in this country is the 
standard Western Union pin-switch, which is shown in 
Figure 69, and which is almost too well known to re¬ 
quire description. 

On the front of the board are placed any required 
number of vertical brass bars in pairs. Between each 
pair of these upright bars is placed a row of brass discs, 
while all the discs on each separate horizontal line are 
metallically connected by means of a coi)per wire, thus 
representing the horizontal series of the bars, the verti¬ 
cal brass bars being the opposite series. Each disc has 
a semicircular hole cut in its edge at each side, and 
each bar has the corresponding semicircle cut opposite 
the hole in the disc, so that a metallic plug put in any 
of the holes presses against both the upright and cross¬ 
bar, thus making the connection. In telegraphic prac¬ 
tice the incoming wire is led to the binding-screw con¬ 
nected to one of the upright bars—for example, No. 1 
—and the outgoing wire connected to No. 2, and so on, 
until all the wires are provided for. The instruments 
are similarly connected to the binding-screws of the 
horizontal bars, or the wire and discs representing the 
same. It is, then, obvious that to connect any line with 
any instrument all there is to do is to put in plugs at 
the point of intersection. For instance, if No. 1 line is 
to be connected to No, 1 instrument, we put a plug in 
the intersecting hole between the first upright bar and 
the first disc, and another in the hole between the 
second upright bar and the disc immediately below the 
first one, or the second one down the column. In this 
class of switch-board the lightning-arrester is usually 


OFFICE WIRES, FITTINGS, ETC. 


199 


placed at the top, in the shape of a brass bar connected 
to a ground-wire, and placed horizontally across all the 
upright or line bars, as close as possible to them with¬ 
out touching. This can also be used as a testing ground 
by means of two pin-holes drilled through it and through 
the edge of the upright bars on each side. To put on a 
ground a pin must be inserted on the necessary side. 



In the figure line 1 is shown connected with its in¬ 
struments by means of two plugs inserted between the 
upright bars and the discs; line 2 is similarly con¬ 
nected with its own instrument, and line 3, in addition 
to being connected with its instruments, is grounded 
by the insertion of a plug in the upper right-hand 
hole. 

When such a switch is used for telephone service the 
horizontal bars are chiefly used as connecting strips be¬ 
tween any two circuits, and in that case each line is at¬ 
tached to only one vertical strip, thence to instruments 
and ground. 

Since the introduction of the telephone the impor¬ 
tance of the switch-board has greatly increased, and 
many improvements have been invented, chiefly relating 
to the modes of connection and manipulation. 







200 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

186. Describe briefly other switches in use. 

Many small switches or circuit-changers are used for 
cut-outs, ground-switches, battery-switches, and kindred 
purposes. They are usually either plug or button 
switches. 

The plug-switch is simply two or more brass plates 
with holes drilled between them, so that by the inser¬ 
tion of a metal plug any two or more plates, with the 
circuits attached to them, may be connected together. 

The button-switch, as shown in Figure 70, consists 

of a lever, A, pivoted at one end to 
a screw, to which the main-circuit 
wire is attached, and of any re¬ 
quired number of buttons, or con¬ 
tact-points, as B, C, each connected 
to a screw and branch wire below 
the base-board, and to any of which 
the lever may be swung, thus con¬ 
necting the circuit to the branch 
required. 

Several such levers may be connected together by an 
insulated cross-bar and worked by the same movement; 
these are called compound switches. Special forms of 
switch are also used in connection with telephones; 
these are popularly known by the names of secrecy and 
automatic switches. The first of these was devised on 
the baseless theory that every person would be on the 
lookout to listen to the conversation of others, and is 
designed to obviate such occurrences. It consists in 
devices whereby a telephones by turning a lever or a 
hook, opens or breaks the line in the direction in which 
he is not about to converse, and at the same time 
connects a temporary ground, completing the circuit 
through his telephone in the direction in which he does 
intend to converse. 

The automatic switch is one in which the removal 
of the telephone changes the circuit from the alarm to 
the telephone, and is in general use. The principle is 




OFFICE WIRES, FITTINGS, ETC. 


201 


clearly represented by Figure 71, in which, when the 
telephone is in its place on the hook, the line is connect¬ 
ed through the signal-bell, but when the telephone is 
removed from the hook the latter Hies up under the in¬ 
fluence of the retracting spring and connects the line to 
the telephone branch. 



187 . What is meant when ice speak of a loop f 

A loop is the technical name applied to a wire which 
branches out from the main circuit to some other point 
(such, for instance, as a branch office), and returns to the 
main line again at or near the same point at which it left 
it. Loops may be either permanently connected to the 
main line—as when a town is situated a mile or two one 
side of the main line, and the line-wire is led from the 
main line to the town and back again to the main line 
on the same poles—or they may be so arranged as to be 
included in the circuit of any desired line. This is usu- 
ally the case when the loop starts from an office. It 
is then led from the switch-board and can easily be 
switched into any circuit. 

188 . What is a lightning-arrester i 

It is an apparatus designed to protect telegraph offices 
































202 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


and tlieir instruments and inmates from injury by atmos¬ 
pheric electricity, which, when it charges the line-wires, 
follows them into the offices during lightning storms. If 
unprotected the fine wire coils would often be burned 
and the operators might also be injured, fatally or other¬ 
wise. The princijile on which nearly all lightning-ar¬ 
resters are made is that lightning, being the discharge of 
electricity of very high tension or electro-motive force, 
will take a short route, even of high resistance, in prefer¬ 
ence to a longer one of much better conductivity, its 
chief object being apparently to get to the ground by 



the quickest possible way, no matter how difficult that 
way may be. It will, therefore, lea]) over an interven¬ 
ing air-space, or force its way through a resistance that 
acts perfectly well as an insulator to the voltaic current, 
which is of much lower tension. Depending upon this 
principle, lightning-arresters are frequently made by 
connecting each wire, as it enters the office, to a screw 
with a sharp point, and adjusting the sharp-pointed 
screws connected with all the wires as close as possible 














































































































































































































































OFFICE WIRES, FITTINGS, ETC. 203 

to, without allowing them to touch, a metal plate, which 
must be connected to the ground-wire. As there is such 
a short distance between the points and the plate, the 
lightning, when it enters, jumps over the space and es¬ 
capes to the ground. A lightning-arrester embodying 
this principle is shown in Figure 72, A and B being the 
line-wires, which, as shown, are attached to segmental 
metal plates ; C and I) are wires leading from the plates 
to the instruments, and Gf is a wire leading from the 
central heart shaped plate to the ground. 

Another arrester, much used in country offices, is 
made by placing two brass plates, connected to the lines, 
upon a larger brass plate connected to the ground, and 
separating them only by a very thin sheet of non-con¬ 
ducting material—paper is the most frequently used. 
Such an appliance is shown in Figure 73. 



Fig. 73. 


Now, when lightning strikes the wires and enters the 
offices it forces its way through the insulating material 
to the ground-plate below, thus effecting its escape. The 
lightning-arrester must invariably be placed between all 
the other apparatus and the line, so that any charge of 
atmospheric electricity coming in on the wires may be 
afforded every facility to pass to earth before arriving at 
the electro-magnets of the instruments. 

189 . What is a cut-out, and what kind is 'preferable for a 
way-station f 

A cut-out is a switch or circuit-changing device used 
in telegraph offices for the purpose of disconnecting the 











204 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


instruments from the line, leaving, at the same time, the 

line perfect and continuous, so that messages can be sent 

and received by I lie offices on either side of the station 

* 

whose instruments are cut out. They are of two general 
classes. First, those in which the instruments are merely 
short-circuited; that is, a shorter path is given for the 
current than the route through the relay, by connecting 
the incoming and outgoing lines by a button or plug. 
Secondly, those in which the instruments are totally dis- 
connected from the line ; that is, when cut out, no metal¬ 
lic connection is left between the line and instruments. 
The latter is by far the most preferable, as it removes 
the instruments from all possibility of danger from at¬ 
mospheric electricity. Where the Western Union pin- 
switch is used the instruments may be cut out at- night, 
or, when leaving the office temporarily, by connecting the 
two upright bars by one or more extra pins or plugs, leav¬ 
ing the two pins connecting the instrument-loop in place. 

When so arranged the loop to the instruments con¬ 
nected with the cross-strips or discs is short-circuited. 
This is a type of the first class mentioned. It may, how¬ 
ever, be converted to a cut-out of the second class by 
simply placing both of the pins connecting the instru¬ 
ment-loop to the upright on the same disc, thus making 

a short-circuit in and out of the 
office, and at the same time 
opening the wire leading to the 
instrument. A simple form is 
shown in Figure 74 ; the line wires 
entering are connected to the 
terminals, L, and the instrument 
wires are connected with the 
binding-screws, B, B. When the 
metal bars, S S, are swung on the terminals, B, the 
circuit includes the instruments; when both bars are 
turned on the middle plate, C, the instruments are cut 
out, and the circuit is completed through the plate, C. 

The most popular and universally employed cut-out 











OFFICE WIRES, FITTINGS, ETC. 


205 


for way-offices where there are but one or two wires is 
the plug and spring-jack cut-out. The plug is a double 
wedge made of two pieces of brass, separated by a thin 
layer of insulating material. 

The spring jack, as shown in Figure 75, consists of a 
brass spring brought very firmly against a stationary 
pin, the spring 
being perman¬ 
ently connected 

t/ 

with one line- 
wire and the 
pin with the 
other. Each of 
the two brass 
pieces compos¬ 
ing the wedge 
is attached by a flexible conductor to one of the instru¬ 
ment-wires, so that the two together form actually a loop 
that can at will be inserted into a spring-jack, which is 
always in the line-circuit. 



190 . What is a spring-jack i 

It is an arrangement for readily inserting any loop 
into a line-circuit, and is operated in conjunction with a 
wedge- connector. 

It was invented first by Messrs. Cooke and Wheatstone, 
and patented by them for use in their needle-telegraph 
system as early as 1837. In 1855 it was adapted for use 
in connection with switch-boards, considerably modified 
in form and improved by G. F. Milliken, of Boston, who 
also employed it as a cut-out. The two line-wires are 
run to two binding-screws at the top of a base-board, 
and from these are connected, by means of small wires 
below the board, one to a strong brass spring, the other 
to a brass pin, against which the spring strongly presses 
by its elasticity. The instrument-wires, connected into 
a wedge or plug such as that described in the last an¬ 
swer, and fitted with a rubber handle, are inserted be¬ 
tween the two surfaces, and by the spring and the con- 








•206 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


stant rubbing a good connection is insured. Somewhat 
varied in form, this device has come into extensive use 
both in telegraphic and telephonic service. Any con¬ 
trivance where a wedge is employed to connect or dis¬ 
connect instruments, or to change a circuit by insertion 
between, or withdrawal from, spring contacts, may pro¬ 
perly be termed a spring-jack. 

191 . What is a relay , hoiv is it made , how used , and from what 
does it derive its name f 

A relay is an instrument included in the line-circuit at 
eacli station, which acts by the influence of the electric 
currents on the main line to bring into play a battery, 
called the local battery, at the receiving station, and, 
by closing the circuit of such local battery, to work a 
sounder or register with much greater strength than it 
could be worked by the main line current, which is, of 
course, much weakened by the distance it has to travel, 
or by the resistance of the long line-circuit it has to 
traverse, as well as by the leakage due to imperfect in¬ 
sulation. It is obvious that such currents, though too 
feeble to work the heavy armature-levers of a sounder 
or a register, may yet be perfectly able to move the 
light lever of a relay-magnet, and thus close the local 
circuit. It is precisely like a key circuit-closer, with 
the exception that it is not worked by hand but by the 
line-current. Professor Wheatstone was the first tele¬ 
graph man who employed the principle, although, in¬ 
stead of using an electro-magnet to operate the circuit- 
closer, lie employed an electro-magnetic needle, deflected 
by being hung in the centre of a coil; the needle was 
provided with a point of metal which closed a circuit 
and rang a bell by dipping into a cup of mercury that 
formed one electrode of an open circuit, the needle 
being the other. 

The relay of the present time is made as follows : The 
electro-magnet is formed of two spools of fine, silk- 
covered magnet-wire, usually No. 32 gauge. These 
each enclose a core of soft iron, and both cores are 


OFFICE WIRES, FITTINGS, ETC. 


207 


united at one end by a soft-iron yoke or heel-piece. 
The wires of the two coils are joined together, so that 
one coil follows the other in the line-circuit, and the 
direction of the wire forming the coils must be so that 
if the cores were bent up, and thus constituted one 
straight bar-magnet, the wire would be in the same 
direction throughout. These coils are placed upon a 
flat base of wood, and the ends of their wires are con¬ 
nected to two binding-screws, usually placed near one 
end of the wooden base. The coils are also fixed with 
the yoke which unites them to face the same end. The 
two coils together will, on an average, have a resistance 
of about one hundred and fifty ohms. In front of the 
free end of the cores is hung on pivots a light brass 
lever, carrying a light soft-iron armature, which is 
immediately opposite to the core ends. This lever vi¬ 
brates between, and is limited in its movements by, two 
set-screws which are set in a brass frame near its upper 
end. The limit-screw which the lever strikes when 
drawn up to the cores and coils that form the elec¬ 
tro-magnet is, by means of the brass frame, one con¬ 
tact-point or terminal of the local circuit. The back 
limit-screw is tipped with some non-conducting sub¬ 
stance, so that when the lever falls back the local cir¬ 
cuit is again opened. The lever itself is connected by 
its pivots or otherwise to the other terminal of the local 
circuit. The wires leading from the lever and from the 
contact point above are led under the base to two other 
binding-screws, and there connected to the local battery 
wires. A retractile spring is attached to the back of 
the armature, and tends to draw it back when not at¬ 
tracted by the magnet. A screw is also fixed at the 
back of the magnet under the yoke-piece, by which 
also the magnets may be withdrawn from or advanced 
toward the armature. 

Figure 76 shows a relay constructed in the manner 
described, and is a type of nearly all the Morse relays 
in use in the United States. 


208 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


To work a relay properly tlie armature movement 
should be very small. This is adjusted by the liinit- 

screws at the top of 
the armature-lever. 
The play between 
these screws should 
never exceed one 
thirty-second of an 
inch ; and the ad¬ 
justment should be 
so made that, when 
the armature is at¬ 
tracted, a piece of 
thick letter-paper 
can be passed be- 
tween the ends of 
the cores and the 
5 face of the arma¬ 
ture. There is an¬ 
other adjustment 
which is more im¬ 
portant, and its pro¬ 
per management, 
especially on badly- 
working lines, is 
one of the best tests 
of a good operator. 
It consists in ad¬ 
justing the re trac¬ 
tile spring by means 
of a screw to which 
it is fastened. To 



do it, it is best to advance the magnet nearly close 
to the armature, so as to take full advantage of the 
strength of current, and then turn up the spring, that 
it may recoil promptly when the main circuit is opened. 
If the armature sticks or lags when the spring is suffi¬ 
ciently tense, the magnets must be screwed a little back. 







































































































OFFICE WIRES, FITTINGS, ETC. 


209 


The name relay is derived from rlie analogy which the 
function of the instrument bears to the change of horses 
and consequent renewal of power at the different stages 
of a long journey. 

Another form of relay is much used in Europe and 
other countries, and, to some extent, on special systems 
in America. It is called the polarized relay. 


192 . Describe briefly the polarized relay and its method of 
operation. 

A 'polarized relay is one in which the retractile spring 
which serves to withdraw the armature-lever from the 
connecting point of the local circuit when the circuit is 
opened is replaced by the attraction of a magnet. As 
the moving armature is very light, and as the attraction 
of one pole is assisted by the repulsion of the other, the 
polarized relay is very sensitive. The Siemens polarized 
relay is the best known of its class. 

Its principal features are represented in Figure 77. It 
is composed of a steel 
permanent magnet bent 
to aright angle—that is 
to say, till it is shaped 
like two sides of a 
square. One end is 
then a north and the 
other a south pole. On 
one end—the end that 
lies flat, or the base of 
the square—an electro¬ 
magnet is screwed, the 
heel-piece of the electro¬ 
magnet lying across the 
permanent magnet. The 
extreme end of the 
other arm, or the up- Fig 77 

right side of the square, 

is forked, and in the fork is pivoted a small soft-iron 
bar, which acts as the lever and armature of the relay. 



















210 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


This turns horizontally on its pivot and works between 
the poles of the electro-magnet, which terminate in flat 
pole-pieces of soft iron. The armature is extended out 
by a slender tongue, the motion of which is limited 
bv a metallic screw forming the local connection on one 
side, and a non conducting screw on the other side. 

The two soft-iron cores of the electro-magnet have by 
induction become charged with magnetism of the same 
polarity as the end of the permanent magnet to which 
they are fixed—say north ; and the armature is similarly 
charged with the magnetism of the end to which it is 
fixed—south, of course ; so that, working between the 
two poles of the electro-magnet, it is, if placed in the 
centre, attracted equally by both of them, but it moved 
the smallest distance to either side it will be attracted to 
that side. If a current of electricity be sent through the 
relay-coils, one of the poles has its induced north mag¬ 
netism strengthened and the other has it weakened or 
neutralized, because the current tends to set up an in¬ 
dependent magnetism of its own in the electro-magnet, 
in one leg agreeing with, and in the other leg opposing, 
the induced permanent magnetism. Now, if the relay is 
to be used in a system of telegraphy which is worked 
by opening and closing the circuit, the relay must be so 
adjusted, by altering the position of the iron pole pieces 
and the limit-screws, that when no current is passing 
the armature shall be attracted to the insulated limit- 
screw strongly ; if a current of suitable direction be 
now sent, the magnetism in the electro-magnet cores 
will be so changed that the armature will be smartly 
drawn over to the other side, closing the local circuit. 
If the current is not of suitable direction it can be 
made so by merely transposing the entering and leav¬ 
ing wires. When the current ceases the armature will 
at once be drawn back to the original side by its su- 
perior magnetic strength. If, however, rlie system of 
telegraphing used be that of sending currents of alter¬ 
nate direction, the armature must be adjusted as nearly 


211 


OFFICE WIRES, FITTINGS, ETC. 

ns possible in the centre between the poles of the electro¬ 
magnet, and in that case it will stay on the side to which 
if was last attracted until drawn to the other side by 
the passage of a current of opposite direction. 

193. TT hat is a Morse telegrapli-key , and how is it made , 
connected , and used f 

The key used on the ordinary closed-circuit telegraph 
systems of this country is simply a device for closing and 
breaking the circuit of the main line, and thus produc¬ 
ing the alternate charge and discharge of the electro¬ 
magnets of the relays included in such circuit. By 
making in this way the alternate breaks and closings of 
different length, number, and disposition, any required 
signal can be sent, and either recorded or sounded at 
any designated point. The key is constructed as fol¬ 
lows : A metallic lever, four or five inches lone;, is liune 
upon a steel arbor between two set-screws attached to a 
metallic frame. It is movable vertically, but its play is 
limited in one direction by its anvil or front contact, and 
in the other direction by a brass set-screw by which the 
degree of play is adjusted. The anvil is insulated by a 
bushing of hard rubber from the frame. One wire of the 
main circuit is connected to the anvil and the other to 
the frame. Screw-legs are attached, one to the base of 
the frame and the other to the under side of the anvil. 
By these screw-legs the wires of the circuit are attached 
and the key is clamped to the table. 

The lever of the key is fitted with a finger-piece of 
hard rubber or ivory, which protects the fingers of the 
operator from electric shocks. The contact-points of the 
lever and the anvil are generally made of platinum, as 
ordinary metals would be burned and melted by the 
electric spark which passes when contact is broken. 
Some advocates have, however, been found for steel 
points. A spring is placed under the lever, which keeps 
it away from the anvil when the former is not pressed 
down ; and as there is then no connection between the 
two wires of the circuit, a switch or circuit-closer is at- 


212 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

tacked, which, when the key is not being used, serves to 
connect the anvil with the frame. The key we show in 
Figure 78 is made as described and is of the most im¬ 
proved character; its lever is very light and is of line 
steel forged in one piece with the trunnions. Keys are 
now made with binding screws attached to their upper 
surface, so as to dispense with the leg connections. 



Fig. 78. 


Keys are also made, and work excellently, with con¬ 
tact-points consisting of two metal discs, one fixed to 
the lever and one to the anvil. The upper disc is placed 
so that its periphery is at right angles to the lower one, 
and the point of contact can be varied, when necessary, 
by turning either disc a short distance round, both be¬ 
ing adjustable. 

This improvement was made by George Cumming, of 
New York. 

In a way-station one wire runs from the key to the 
relay, the other wire from the other leg of the key to 
the switch-board or cut-out, and thence to the line. 
W hen the key is to be used the switch or circuit-closer 
is first opened. As soon as this is done the circuit is, of 
course, open, the anvils forming one end of it and the 


























OFFICE WIRES, FITTINGS, ETC. 


213 


contact-point of the lever the other. The current, there¬ 
fore, cannot pass, and the armatures of all the relays in 
the circuit cease to be attracted and fall back. The 
operator then alternately depresses the lever and al¬ 
lows it to rise under the influence of the spring, in cor¬ 
respondence with the signals of the Morse alphabet; 
and, in exact harmony with such movements, the circuit 
is closed and broken ; the armatures of the relays in the 
circuit are attracted and withdrawn, and the strokes of 
the sounder—or, technically speaking, the dots and 
dashes of the register or recording instrument—are pro¬ 
duced by the closing of the local battery circuit, which 
is operated by the movement of the relay armatures. 

194. Are any other keys in use besides the ordinary closed- 
circuit key already described t 

Yes ; several others. What is called the open-circuit 
~key is used on some lines, and is generally employed in 
most European countries. In general principles it re¬ 
sembles the key already described. The chief point of 
variation is that both back and front contact-points 
form electrical connections. When the key rests on the 
back contact the line is‘generally completed through the 
relay to the ground or out to the next station. When 
the key is dejiressed to the front contact the battery is 
connected to the line. Other keys are made to close on 
the back contact, thus opening the circuit entirely when 
they are depressed. Others, again, sometimes called 
pole-changers, or reversing keys, are constructed and 
connected to reverse the direction of the battery current 
at each alternate depression and retraction. An alter¬ 
nate-current key is easily constructed by fastening to a 
base of non-conducting material two springs of metal 
having finger-pieces of hard rubber. Over these, and 
pressing against the back of both springs, is a metal¬ 
lic bridge. The springs by their elasticity press firmly 
against the bridge. Immediately below the knobs or 
finger-pieces is an anvil of metal. One pole of the bat¬ 
tery is then connected to the anvil and the other to the 


214 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

bridge, while one of the spring keys is connected to the 
line and the other to the ground. Now. when one key 
is pressed a current of one direction is sent to the line, 
and when the other key is pressed a current of the op- 
posite direction is sent to the line. 

195. What is a sounder, and how is it connected % 

The sounder is a very simple instrument and ie(^uiies 



no protracted explanation. It is generally used in short 
local circuit and is operated by the armature of the re¬ 
lay. On short lines, however, sounders wound with 
suitable wire are often connected in the main circuitj 















































































































OFFICE WIRES, FITTINGS, ETC. 


215 


Riid tlie relay is then omitted. It is merely an upright 
electro-magnet screwed down to a base-board and fitted 
with a soft-iron armature which is provided with a lever 
working in adjustable pivot-screws. Its free end is 
limited in its stroke by two set-screws. The lower screw 
is set so that the armature almost touches the face of 
the magnet-cores, and the upper screw is set far enough 
away to give a sufficiently loud sound ; a retracting 
spring is attached to the lever and pulls it back when it 
is not attracted by the magnet. The signals are given 
by the beats of the lever between these two screws, and 
the different signals are distinguished by the difference 
in sound between the down and up stroke of the lever 
and the duration of the strokes. The magnet, when 
used in a local circuit, is wound with No. 24 silk- 
covered copper wire, and has a resistance averaging 
about four ohms. 

The sounder we show in Figure 79 is the Giant 
Sounder, designed by J. H. Bunnell. 

When the armature of the relay is attracted by the 
closing of a key in the main line, the local circuit is 
closed by the relay contact-points, the sounder-magnet 
is charged by the local battery current, the armature is 
attracted, and the lever is smartly drawn down and the 
down stroke is made. When the relay armature falls 
back the circuit is once more opened, and the spring 
pulls the lever back, causing the up stroke. The sound¬ 
er-stroke is much improved by screwing the instrument 
down to the table. One of the binding-screws must be 
connected to one pole of the local battery, the other to 
one of the local binding-screws of the relay. 

196. What is a register , and how is it connected f 

The register is the name given in America to the Morse 
recorder. It is made in several different ways, all of 
which, however, involve the same principles. The pur¬ 
pose of this instrument, which is represented by Figure 
80, is to record the characters of the Morse alphabet on a 
strip of paper. It w r as the original idea of Professor 


216 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

Morse to do this, and the sounder is a natural outgrowth 
and extension of this principle. Two objects are to be 
accomplished by the register—first, to record the charac¬ 
ters ; and, second, to draw the paper along so that the 
characters will be made in regular succession. To effect 
these results the paper, which is in the form of a roll 
near or over the register, is passed between a pair of 
rollers, r, which are revolved by a train of clockwork 
driven by a weight attached by a cord to the drum, W. 

The clockwork is started or stopped by a brake, a. 

The upper roller has a groove cut in it all the way 
around, so that the stylus, p, may readily emboss the 
paper by pressing it into this groove. 



c. 


Fig. 80. 

The electro-magnet, M, is placed upright; itsnrmature 
is furnished with a long lever, L, and at the end of the 
lever is fastened a steel point, or style, p , which may be 
adjusted up or down by a set-screw. 

The strip of paper passes through the guide, cp and be¬ 
tween the grooved rollers. The steel point is adjusted 
immediately under the groove in the upper roller, and is 
on the under side of the passing paper. 

A spring retracts the armature when no current is pass¬ 
ing, just as in the relay or sounder. Every time the re¬ 
lay points are closed the register armature is attracted, 























OFFICE WIRES, FITTINGS, ETC. 


217 


and as the armature end of the lever goes down the style 
(being on the other side of the pivots, which are support¬ 
ed by set-screws) goes up, a mark is made upon the 
paper by the point, corresponding in length to the dura¬ 
tion of the passage of the current. The magnet is wound 
with silk-covered copper wire of No. 23 or 24 gauge, and 
is ordinarily of about four ohms resistance. Two large 
cells of gravity battery ought to work it well. Main-line 
registers are sometimes employed for lines not exceeding 
in length twenty or thirty miles. They must, of course, 
be wound with much finer wire. 

The register is not at present used to any great extent 
in America, having been superseded by the more simple 
sounder. In small country offices it may, however, be 
seen in all its glory. Had it remained in universal use 
it would probably by this time have developed into the 
ink-writing instrument, which is much used in Europe. 
The connections are made exactly the same as those of 
the sounder. 

197. It is required to connect a sounder and register with 
a three-point switch , so that either can he worked by the relay; 
Jioiv is it done % 

We will suppose the relay, register, and sounder to 
be already fixed upon the table and the local battery 
set up. Connect one pole of the battery to one of the 
relay local connections, 
and the other relay 
binding-screw to the 
lever - point of the 
switch. Attach one of 
the other points of the 
switch to a register 
binding post, the other 
to a sounder binding- 
post. Then run a wire 
from the other register-post to the remaining sounder- 
post, and from there to the other pole of the battery, 
and it is done. To work the register the switch must 


















218 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


be turned to one point; to work tlie sounder, to the 
other. 

This is shown in diagram by Figure 81. 

198. What are repeaters f 

Repeaters are peculiar arrangements of instruments 
and wires whereby the relay, sounder, or register of one 
circuit is caused to open and close another circuit, thus 
repeating or duplicating the signals sent on the tirst cir¬ 
cuit, by the hand of the operator working a Morse key, 
on to the second circuit by the upward and downward 
movements of the instrument armature-lever, in the 
same way that a relay closes the local circuit of a sound¬ 
er or register. The earliest ones were so arranged that 
but one side had facilities to repeat; and if the receiving 
operator desired to break he was dependent on the at¬ 
tendant at the station where the repeater was located to 
turn a switch whereby the repeating devices were trans¬ 
ferred to his circuit. This had obvious disadvantages, 
and many automatic repeaters have been invented which 
do not need the services of an attendant, as by their use 
either side can send, either circuit repeating into the 
other at will. Repeaters are used to connect two cir¬ 
cuits together to work through which are ordinarily 
operated separately ; and by their use direct communica¬ 
tion lias been had from Heart’s Content, Newfoundland, 
to San Francisco. They are also often used for connect¬ 
ing branch lines with a main line. The lirst repeater 
was used for this purpose, and was designed and put 
into operation at Auburn, N. Y., to repeat press news 
from that office to Ithaca, 

199. What are the repeaters which up to the present time have 
been invented t 

The first was the one previously alluded to, and is 
universally known as the button-repeater. It was 
planned by Merritt L. Wood in September, 1846. The 
next was the open-circuit repeater of Charles S. Bulk- 
ley, devised in 1848, which enabled messages to be sent 
direct between New York and New Orleans Farmer 


OFFICE WIRES, FITTINGS, ETC. 


219 


and Woodman in 1856 invented the first automatic 
closed circuit repeater, while after this in rapid succes¬ 
sion came the automatic repeaters of Hicks—who has 
invented no fewer than three different forms of re¬ 
peaters—Clark, Milliken, Toye, Gray, Haskins, Bun¬ 
nell, and Gerritt Smith. The last one produced was 
that of Catlin. All of these have their special virtues, 
and have each been more or less used, but only a few of 
them are now in operation. 

200. State which repeaters are now most frequently used. 

Wood’s button-repeater, though the oldest, is still 
much used on account of its simplicity and the readi¬ 
ness with which it is constructed by amateurs or in 
offices without special facilities. It is simply a switch 
which is capable of being placed in either of three posi¬ 
tions. In one of these positions each line is connected, 
through a ground-switch, with a common ground-wire. 
In a second position the armature-lever of each of the 
sounders is interposed in the circuit of the other line so 
as to operate as an electro-magnetic key. The third posi¬ 
tion is but the second reversed. It needs an attendant 
all the time, as it can only be worked from one direction. 
When the receiving operator wishes to break he opens 
his key or makes dots, and the attendant, seeing that 
the sounders are not working together, turns the button, 
permitting the receiver to become in his turn the sender. 
When it is desired to work the two lines through as one 
it is only necessary to throw off the ground-switch. 

The connections are clearly shown in Figure 82. M, 
M' are the relays of the two circuits, S S' their sounders, 
B and B' the main batteries, 4 the ground-switch, E 
and W the east and west line-wires. When the lever, L, 
is in the position shown the wires are arranged as two- 
independent circuits. To make a continuous through 
circuit the lever, L, is left untouched, but the ground 
switch, 4, is thrown off. To arrange the two circuits for 
repeating, the ground-switch, 4, is closed, and the lever, 
A, placed either on the plates 2 2 or 3 3. In the 


220 


ELECTRICITY, 


MAGNETISM, AND TELEGRAPHY. 


former position tlie eastern line repeats into the west¬ 
ern, and in tlie 
latter position 
the western re¬ 
peats into the 
eastern circuit. 

The automa¬ 
tic repeaters 
which are now 
most generally 
used are those 
of Milliken, 
Toye, Bunnell, 
and Haskins. 
The chief aim 
of all of them 
is to give the 
power of break¬ 
ing, sending, and receiving to each circuit alike, and the 
great difficulty in the way lias been to keep the arma¬ 
ture of the relay of the receiving wire quiescent, and 
at the same time have it so arranged that it, would 
promptly come into action when a break was made. 
This has, however, been successfully accomplished in 
many ways.* 



Fig. 82. 


An operator sending through a repeater must send 
firmly and heavily, and make long dots and correspond¬ 
ingly long dashes, because the lever of the repeating 
instrument requires an appreciable amount of time to 
make its stroke, and each repeater on a single line of 
communication shortens the current still more. For 
this reason the repeater-levers must be adjusted to as 
short a stroke as possible. 


201 . Was there not a very simple repeater devised by Edison f 
Yes. It is described in Pope’s “ Modern Practice of 


* A full description of nearly all tlie repeaters that are, or have been, in 
use can be found in Davis and Itae’s invaluable “ Hand-book of Diagrams 
And Connections.” 






































221 


OFFICE WIRES, FITTINGS, ETC. 


WEST 



the Electric Telegraph,” and also in the “ Hand-book of 
Diagrams and Connections ” already referred to, and is 
shown in diagram 
by Figure 83. It 
is a very conve¬ 
nient button-re¬ 
peater, has been 
found serviceable, 
and can be fitted 
up very quickly, 
as it needs no 
apparatus except 
the regular relays 
and sounders and 
a common two- 
point ground- 
switch. To set it 
up, the line, say 
from the west, is connected first with its own relay, M 
thence it passes to the point 3 of the ground-switch, 
and through the local points of the opposite relay to the 
main battery, E, and ground, Gr. The other line is simi¬ 
larly connected ; the main post of the ground-switch. S, 
is then connected with one pole of the local battery, E'. 
The other pole of the local battery connects with the 
sounder, L, passing from the second binding-screw of the 
sounder to the wire 1, which connects the two sets of re¬ 
lay-points with the ground. The sounder and local bat¬ 
tery form a portion of both local and main circuits. 
When the button-switch is turned on to the point which 
touches the eastern circuit the eastern circuit repeats 
into the western, while the western relay works the 
sounder, and vice versa. 


Fig. 83. 





























CHAPTER XY. 


ADJUSTMENT AND CAKE OF TELEGRAPH INSTRUMENTS. 

202. What is usually meant by the “ adjustment ” of a re¬ 
lay l 

Tlie adjustment of a relay means the adjustment of 
its vibrating armature, both as regards its distance 
from the magnet-cores and the space through which it 
vibrates, or the length of its vibration. The lirst ad¬ 
justment is regulated by the screw working the retract¬ 
ing spring of the armature, by the screw working the 
advance or withdrawal of the magnet, and by the front 
limit-screw, which also forms the contact-point of the 
local circuit. The latter adjustment is made by the two 
limit or set screws, between which the lever plays. 

Ordinarily a relay should work well when adjusted 

as follows: With key open, or instruments cut out, lix 

the front limit-screw so that a moderately thick piece of 

letter-paper can be inserted between the armature and 

magnet-cores. Then screw up the back limit-screw till 

it is as close as possible, leaving an almost imperceptible 

movement to the lever. Then screw up the magnet 

until it is less than a sixteenth of an inch, place 

the instrument in circuit, and turn up the retracting 

spring. If the armature now sticks to the magnets 

turn up the spring still more ; and if, when it is turned 

up pretty high, the action of the magnet is still too 

strong, the magnet must be withdrawn a little. W T e 

have seen operators who uniformly work with a 

slack retracting spring and magnet turned away back; 

but this is against common sense, for, to get the full 

222 


ADJUSTMENT AND CARE OF INSTRUMENTS. 223 

benefit of the line current mid to make tlie relay work 
quick and sharp, it is obvious that the magnet should 
be as close to the armature as it can be without sticking, 
so that it may advance sharply when the circuit is 
closed ; and also that the spring should be adjusted 
high, so that the armature shall fall back promptly 
when the circuit is broken. Correct adjustment is one 
of tlie never-failing signs of a good operator, and it 
often, especially in wet weather and on way wires, 
demands great skill and attention. 

203. T Vhy is it that the adjustment of the relay is very diffi¬ 
cult on some lines in wet weather t 

Because in wet weather the escape of current from 
the line at each insulator (which even in the best-in¬ 
sulated lines is always present in some slight degree) is 
greatly increased and varies frequently, rendering the 
magnetism of the relay correspondingly uneven, being 
now stronger and again weaker. 

This is especially the case in lines where the insula¬ 
tion is defective to commence with, and on some long 
way circuits it has often occurred that during a rain¬ 
storm it has been totally impossible to work the wire at 
all, or only in sections of a few miles in length. 

The condition of the telegraph lines of America lias 
been so much improved during the last ten years that 
such cases have now happily become rare. 

204. Why is it that during wet weather on badly working 
wires the relay often remains still when a distant station is 
sending , and why is it necessary to adjust high in order to get 
such stations f 

This is chiefly noticed on lines where the battery is 
divided, part of it being at one end and part at the 
other. As most of them are so arranged, it is a very 
frequent occurrence on lines of any great length. It 
is caused by the escape from the insulators which are 
between the station working and the station where the 
relay fails to respond. This becomes so considerable, 
by the aid of the wet insulators and poles, as to act the 


224 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

same as if an average country ground-wire were put 
on; and the current from the nearer main battery (if 
both batteries are equal in size) now has a circuit from 
the ground at the terminal station where it is located, 
over the line through the relays which remain still, to 
the escape arising from the united effect of leakage at a 
great many insulators at once ; and the current in this 
artificial circuit produces sufficient magnetism in the re¬ 
lays to hold the armatures forward when the adjusting 
spring is at its usual tension, even when the current 
from the more distant battery is interrupted and the 
line opened by the key which is being worked at the 
distant station. This phenomenon can occur in either 
direction when a battery is placed at both ends, but 
only in one direction when the battery is at but one end 
of the line; for it is obvious that if a circuit have a 
battery at only one end, any office, by opening a key, 
cuts off the current from the entire line beyond it, and 
the armatures of nil the relays beyond must, in conse¬ 
quence, fall back. Sometimes, therefore, in hard-work¬ 
ing lines, where there is much escape during a rain-storm, 
the battery is taken off one end. When a relay, at its 
ordinary adjustment, refuses to respond to the signalling 
of a distant station, the spring must be adjusted higher, 
so as to put a greater strain on the armature, in order 
that it may overcome the attraction of the magnetism 
due to the escape. It will then respond to the breaks 
of the distant station. If the escape be still felt the 
magnet must be withdrawn a little by the back screw. 

205. What is the best method of adjusting on a liard-icork- 
ing line in wet weather f 

The best general way to adjust, both in wet and 
dry weather, is the common-sense method, Which is 
as follows: 

The limit set-screws should be so adjusted that when 
the armature is attracted it will almost touch the mag¬ 
net-core, allowing just space enough to insert a piece 
of stout writing-paper between. This done, adjust the 


ADJUSTMENT AND CARE OF INSTRUMENTS. 225 

back limit-screw up so close as to allow of the least 
possible motion necessary to open tlie local circuit. 

Screw up the back adjustment till the magnet is quite 
close to the armature ; still, however, being careful that 
they do not touch. This is so that all the current on 
the line may be utilized on the magnet. Then screw the 
adjusting spring up till the tension is quite strong, thus 
giving the armature all the chance possible to fall back 
every time the main circuit is opened. If breaks still do 
not show clear on the sounder or register, the magnet 
must now be screwed back a little. 

We may suppose the relay to be adjusted to be 
located at a station fifty miles from one terminal or 
repeating office and two hundred miles from the other. 

In such a case it is probable that the greater part of 
the business will be to and from the former ; and the 
best plan will be to keep the instrument so adjusted 
that the sending of the near repeating office comes light 
yet perfectly distinguishable. The call from that office, 
and all between it and the receiving station, may then 
be readily heard, while the heavy sending of the other 
terminal station and other distant stations have also a 
good chance to be heard. In any case, however, before 
opening the key in bad weather the adjustment should 
be pulled up, so that, if any distant station is using the 
line, its sending may be made manifest as the tension of 
the spring is increased. 

206. Why does a key sometimes stick , and what should he 
done to remedy a sticking key f 

When a key, on rising, does not break the circuit it 
is said to “ stick.” This sticking is generally caused 
by its platinum contacts becoming gradually burned and 
made rough by the repeated action of the spark which 
appears every time the circuit is broken, or by very 
small specks of metallic dust, which collect round the 
anvil and points. Sometimes it is occasioned by spongy 
or soft platinum having been used as the material for 
the contacts. This fuses to a certain degree every time 


226 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

the key is opened. In either case a partial and imper¬ 
fect connection is produced between the two parts of the 
key, which should be completely insulated from one 
another when the key is opened. 

When sticking occurs it can usually be remedied by 
rubbing the points with line emery-paper. If that does 
not cure it a line tile may be very carefully employed, 
but only until a new surface is made. Frequent use of 
the lile should, however, be avoided. 

An inexperienced operator is often liable to mistake 
other troubles for a sticking key. 

Dirty relay-points will, for example, so far as the 
register or sounder is concerned, act in precisely the 
same manner, and must also be cleaned with tine 
emery or sand paper. 

Loose pivot-screws will often make trouble with a 
key, and should not be tolerated; the pivot-screws 
should always be kept as tight as is consistent with 
a free and easy movement of the key. 

If a key has soft or spongy points there is no radical 
cure until the points are renewed. 

In such a case the only way to make the key work 
at all is to give the lever considerable play when work¬ 
ing it, and to clean the points frequently. 

Keys with soft points are now happily rare. 

207. What precautions are necessary to get good icorlc from a 
sounder i 

First and foremost, the sounder magnet helix should 
have about the same resistance as the local battery. If 
the battery consists of two cells of the gravity form, 
the sounder coils should have a resistance of about four 
ohms. 

The sounder has three adjustments: one by which 
the play of the armature-lever is regulated, one by 
which the distance of the armature from the magnet- 
cores is regulated, and one determining the degree of 
tension of the retracting spring. 

To adjust a sounder the armature-lever is first made 


ADJUSTMENT AND CARE OF INSTRUMENTS. 227 

to work easily and yet snugly upon its pivots, which are 
then locked by their set-nuts. Then the armature is 
fixed by the screw so that a piece of thick writing-paper 
can be passed between the core and the armature. 

The sciew regulating the stroke is then brought to a 
suitable distance to give the proper length of stroke, 
after which the retracting spring is screwed up, so that 
when the circuit opens the lever is pulled sharply 
back against its back limit-screw. If it now sticks 
when working, the spring must be tightened; if the 
spring is already tight the front limit -screw may be 
screwed up a little, thus bringing the armature to a 
point further from the core. 

TV hen a sounder gives a satisfactory sound it should 
be let alone. 

A sounder should always be screwed down to the 
table, which then forms a sounding-board. 

If a sounder has always worked well, but at length 
commences to stick, the adjustments should all be in¬ 
spected to see if they are tight; if they are, the defect 
is probably due to residual magnetism in the cores, 
which may be measurably rectified by reversing the 
wires. 

Care must be taken not to break or bend the fine 
magnet-wires in cleaning or dusting the instrument. 

208. How should a register be managed t 

The adjustments already described as belonging to 
the sounder are all of them in the register also. Be¬ 
sides these we find others—viz., that by which the 
rollers which draw the paper along are regulated, and 
the adjustment of the stylus, or pen. 

The length of stroke, distance from cores, and tension 
of retracting spring are adjusted exactly in the same 

way as in the sounder. 

«/ 

To fix the pen-point correctly, first adjust the arma¬ 
ture, screwing it to the proper distance from the core, 
then hold it there by closing the local circuit, at the 
same time letting the register run, and screw up the 


228 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

pen-point until it makes a mark on tlie paper which is 
plainly seen, then tighten up the set-nut. 

The mark should only be deep enough to be distinct. 
The limit-screw regulating the stroke must allow the 
pen to just clear the paper when the circuit opens. If 
the paper runs crooked one end of the rollers presses 
tighter than the other, and the end that carries the 
paper fastest must be unscrewed a little. When the 
armature clips or sticks the relay needs adjusting. 

The lever should never be allowed to work loose in its 
pivots, as that would cause irregular dashes, sometimes 
too deep, and at other times not deep enough. The 
paper guides must be just wide enough to allow tlie- 
paper to pass through easily. If the register-lever does 
not respond to the movements of the relay there is 
some defect in the local circuit—very likely a loose con¬ 
nection, a weak battery, or dirty relay-points. 

A register should be kept clean, but never taken to 
pieces out of curiosity; ninety-nine troubles out of a 
hundred met with by young operators are due to un¬ 
necessary tinkering with the instruments. 

209. When and how should a ground-wire at a U'ay-station 
be used t 

A ground-wire should be used on a telegraph line 
only when the circuit is found to be open. It should 
then be used first as a testing wire, to ascertain on 
which side the line is open, and afterward put on, and 
left on, at the side of the instruments on which the 
trouble is found to be. A hen used as a testing ground 
it must be touched to both of the leading-in wires. If 
when touching either side it causes the relay to attract 
its armature, that is the side on which the trouble is, 
and that is the side on which it must be temporarily 
left; thus cutting that station in on the unbroken frag¬ 
ment of the line to the terminal station. 

A hen the line is in working order* the ground-wire 
should be left untouched. It is too much the practice 
among operators at way-offices to put on the ground- 


ADJUSTMENT AND CAKE OE INSTRUMENTS. 229 


wire for any or no cause, but it is a liabit tliat cannot 
be too strongly reprehended. 

210. Give some hints on the general care of a way telegraph 
station. 

Operators at way telegraph stations are frequently 
young and inexperienced. A few general hints may, 
therefore, not be out of place here. 

After lightning-storms the arrester should always be 
examined to see if any damage to it lias ensued. If so 
it should be fixed at once. If that kind of lightning- 
arrester is used in which a thin sheet of paper separates 
the ground from the line plate, the paper ought to be 
renewed, whether damage is apparent or not. 

In bad weather the relay-spring should always be 
pulled up before the key is opened, to ascertain whether 
any one is using the line. 

The motion of the relay armature-lever should be 
kept as small as possible, and the local points of the 
relay kept clean. The armatures, both of the relay and 
sounder, or register, must never be suffered to touch the 
cores of the magnet. 

Every binding-screw about the office ought to be tried 
occasionally to see if it is tight, as the good working 
of the entire line often depends on this. Every loose 
connection introduces a high resistance into the circuit 
of which it forms a part. 

When the instruments are working satisfactorily 
they should be left strictly untouched. 

If the instrument table be covered with an oil-cloth, a 
space should in all cases be cut clear for the key, so 
that the latter will rest on the table. Many escapes 
have been traced to an oil-cloth table-cover. 

All pivots should be just tight enough to prevent 
lateral play. This applies both to keys and sounders, 
or registers. 

If an ordinary Daniell battery with porous cups be 
used for a local, it should be cleaned at least once a 
month. The zinc should not be allowed to touch the 


230 ELECTKICITY, MAGNETISM, AND TELEGRAPHY. 

bottom of the porous cup. In cleaning such a battery,, 
half of the clear liquid may be poured from the porous 
cup, and, after the cup is emptied and cleaned, poured 
back to form the zinc solution. If all the liquid is 
emptied it will be some time before the battery works 
up to its full strength again. 

If a gravity battery be used the cleaning does not 
need to be nearly so frequent. 


CHAPTER XVI. 


CIRCUIT FAULTS AND THEIR LOCALIZATION. 


211. What are the faults most likely to occur on a Morse 
telegraph line, ancl how are they most frequently caused t 

Open wire or complete disconnection, partial or oc¬ 
casional disconnection, dead earth, swinging or occa¬ 
sional earth, escapes, crosses, swinging crosses, wea¬ 
ther-crosses, and defective ground at the terminals. 

Complete disconnection, familiarly called a “break,” 
occurs when the circuit is ojien at any point, and till 
repaired puts an entire stop to communication. It 
may be caused in a variety of ways The terminal 
ground-wire may be broken or cut, the battery may be 
defective, a key may be, and often is, left open, the 
line-wire may be broken—this may occur in many ways 
—or a wire may be accidentally pulled out of a binding- 
post in a station. 

Partial disconnection occurs when the resistance of a 
circuit is greatly increased, and is also caused in a va¬ 
riety of ways. A rusty or otherwise bad joint on the 
line-wire, a wire loose in a screw-post, an imperfect 
terminal ground-wire, or a very bad main battery will 
cause this trouble; and it manifests itself by causing 
the instruments in circuit to work in a feeble and irregu¬ 
lar manner. 

Dead, earth, in American phraseology, is called a 
“ground.” It occurs when the line at any point touches 
the earth, or some good conductor in contact with the 
earth. When the resistance of such a fault is very low 
indeed it practically divides the line in two parts, each 
terminal station working on its own battery to the fault. 


232 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

If only one station lias a main battery the relays be¬ 
tween that station and the fault will work stronger than 
usual, because the total resistance of the circuit is de¬ 
creased ; while the instruments beyond the fault will be 
apparently out of circuit, and will act as if the line were 
open. If there is a battery at both ends the stations on 
each side of the ground will be able to work, but those 
on one side will be unable to communicate with those on 
the other. This trouble may be caused by contact with 
a wire running to earth, or by the line-wire lying across 
a tree or roof ; but is oftenest caused by operators in 
way-offices, who attach a ground-wire to the line for no 
sufficient reason, and forget to remove it. 

A swinging or occasional earth is of the same charac¬ 
ter as the preceding fault, with the exception that in¬ 
stead of being a permanent interruption it comes on only 
at more or less regular intervals. It is a serious fault, 
and often difficult of localization, as such a ground fre¬ 
quently does not stay in long enough to enable it to be 
tested. It is usually caused by the line-wire swinging, 
under the influence of the wind, against some conducting 
substance in contact with the earth, such as a guy-wire. 

An escape is also of the same general character as a 
ground. The difference is only one of degree ; for while, 
in the case of a dead ground, nearly all the working 
current leaves the line at the fault, only a portion does 
so in the case of an escape. It is, in fact, simply a 
branch circuit of comparatively low resistance, by which 
a certain portion of the current of electricity escapes or 
leaks to the earth at the wrong place, thus weakening 
the line current beyond the fault, and strengthening it 
between the main battery and the fault. It is caused by 
defective insulation of the line, instruments, or battery, 
or by contact with an imperfect conductor, such, for ex¬ 
ample, as a tree. 

A cross occurs when two wires come into contact, and 
is generally caused by the wind or by swaying branches 
of trees. A\ hen two wires are crossed a message sent on 


CIRCUIT FAULTS AND THEIR LOCALIZATION. 233 


one is repeated on the other, so that neither one can be 
woiked without interfering with the other. In such 
cases the means adopted is to open one wire on each 
side of the cross until the cross can be cleared. 

A swinging or intermittent cross occurs where one or 
more wires are too slack between the poles or supports, 
so that they are often blown one against the other. This 
trouble is an annoying one, as it is very difficult to 
locate, for the same reason as that given in describing 
the intermittent ground. It is of frequent occurrence 
among the short house-top lines of cities. 

A weather-cross sometimes occurs in wet weather 
from defective insulation. In such cases the moisture 
on the insulators and cross-arms enables the electricity 
to escape or leak from one wire to another. The evil 
effect of this trouble is much lessened by earth-wiring 
the poles. 

Defective ground terminals act as if all the wires run¬ 
ning to ground at the same place were crossed together. 
It is frequently caused by the severance of a gas-pipe 
which is used for the common earth connection. It is 
also sometimes caused by such a pipe being an imper¬ 
fect conductor, or by the connection of the wire to the 
pipe being imperfectly made. 

212. Hoie does a disconnection, or break, make itself appa¬ 
rent, and how is it to be tested fori 

If the line is broken at any point the armatures of all 
the relays at once fall back, and no work can be done 
until the line is repaired. If the trouble is caused by an 
open key the operator at that station will probably 
sooner or later discover it and close it. But if the line- 
wire is broken at any point a lineman will have to be 
sent out as soon as the trouble is located between two 
stations. 

As soon as the circuit is discovered to be open the 
operator at each way-station should connect his ground- 
wire first with one side of the instrument and then with 
the other. If connecting it on either side closes the 


234 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


circuit it shows that the trouble is on that side, because 
on such connection the break is cut off and the line 
virtually terminated at the ground-wire, cutting the 
instruments in. 

In Figure 84, which represents a line with four sta- 



B 




Fig. 84. 


tions, A, B, C, and D, the wire is supposed to be broken 
at F. When B and C attach their ground-wires, as- 
shown and described, it will be seen that two distinct 
circuits are formed : A then being able to work with B, 
and C with D. The fault is thus shown to be between B 
and C. 

If the application of the ground-wire fails to close the 
circuit on either side, the trouble is either in the office, 
or the ground-wire that the operator is testing with is 
defective, or some other office has already closed the 
circuit by the connection of a ground-wire. Hence an 
operator should always, after testing with the ground- 
wire, make sure by a careful search that the trouble is 
not in his own office. 

As soon as any office discovers on which side the line 
is open its duty is to report the facts to the remaining 
terminal station, and from it receive instructions whether 
or not to keep the ground-wire on. Failing such instruc* 
tions, a good plan is, if there are many stations between 
the way and terminal station on the complete side, to 
keep the ground on and frequently remove it tempo¬ 
rarily to see if the circuit has closed; but if the said 
way-station is near to the terminal station on the side 
which is unbroken, it is better to keep the ground off, 
because the greater number of stations are beyond ; and 













CIRCUIT FAULTS AND THEIR LOCALIZATION. 235 


wlien any one of the way-stations lias a message to send 
it can then connect a ground-wire and send it. 

A break is often tested for with a galvanometer, the 
general principle of such a test being the comparison 
of the known insulation resistance when the line is com¬ 
plete with the insulation resistance from the terminal 
stations to the broken ends. It is, of course, a matter of 
absolute necessity to test for a break in a submarine 
cable in this or in a similar manner. 

213. What method may he adopted on short city lines of 
special systems, such as American District or stock-printer 
lines i 

The quickest and most satisfactory way is to put on 
to the broken line a battery of sufficient strength, and 
then have an inspector or lineman go from station to sta¬ 
tion, grounding each instrument for an instant as he 
goes along, until he reaches an instrument which, when 
grounded on the side away from the office, does not 
work, or on which, if a light battery is used, he can taste 
nothing. He has then passed the break, and, retracing 
his steps to the last station, he there attaches a ground, 
leaving it connected until the break thus located be¬ 
tween two stations can be repaired. 

214. What are the effects of an intermittent disconnection , 
and how may such a trouble he located f 

An intermittent disconnection is frequently by inspec¬ 
tors and linemen called a swinging break. It often oc¬ 
curs from a loose connection, a hook-joint which is al¬ 
ternately tightened and loosened by the wind, or, in the 
case of covered wire, it may be caused by the conductor 
being broken inside the covering. On ordinary lines it 
will occasionally make itself apparent by the sound of a 
dot on the sounder, and it sometimes proves very annoy¬ 
ing to operators by opening the circuit for an instant 
while a message is being sent. On printing circuits it 
shows by the instruments missing a beat, and then 
“ throwing out,” causing the printed slip to write 
nonsense, while on District circuits and the like a long 


236 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

dash is produced on the register-tape and the bell 
rings. 

The most satisfactory way, and the only method to be 
depended on, for the location of a trouble of this charac¬ 
ter, is to cross-connect the defective wire with another 
at an intermediate station. This method may be adopted 
on either long or short lines, and is as follows: It is 
better, for the sake of celerity, to make two cross-con¬ 
nections at once. For example, we will suppose two 
parallel lines, No. 1 and No. 2, both running into sta¬ 
tions A, B, C, and 1), and that No. 1 has an intermittent 
break. At the point where the wires leave station A 
interchange them so that No. 1 inside the office connects 
with No. 2 outside, and vice versa. Duplicate the change 
also at station C. No. 1 is then temporarily No. 1 from 
its initial ground at A to the window, No. 2 from there 
to the switch at station C, and again No. 1 from C to the 
terminal ground. No. 2 is, of course, correspondingly 
changed. Suppose now the fault is between B and C 
on No. 1 ; the trouble will be found to have moved over 
to No. 2 at the terminal stations A and D, because 
that portion of No. 1 in which the fault is located has 
by cross-connection been transferred to No. 2 circuit. 
When this is ascertained the wires at the distant sta¬ 
tion C may be straightened and the cross-connection 
changed to station B. Supposing still that the fault is 
between B and C, it will, the next time it comes in, be 
found to have changed back to No. 1, because that sec¬ 
tion of line has been transferred back again to No. 1. 
Now, when thus located between two stations, it can 
generally be easily found by a lineman. If it is, how¬ 
ever, still troublesome, and cannot be found, the lineman 
will have to cross-connect between stations. 

215. How should a partial disconnection causing an ex¬ 
tremely high resistance he tested fori 

The method of cross-connection described in the an¬ 
swer immediately prior to this is the most satisfactory 
course to pursue when only the ordinary telegraph in- 


CIRCUIT FAULTS AND THEIR LOCALIZATION. 237 


struments are at liand. If, however, a good galvano¬ 
meter and rheostat can be readily obtained, a quicker 
way is to employ them, especially if the fault is con¬ 
stant. It will be of great assistance to the tester, in this 
operation, if the resistance of the line at ordinarv times 
is known ; but even if it is not it can usually be calcu¬ 
lated. First measure the suspected line, and see what 
the resistance is with the fault in; then have a good 
ground put on about half way to the terminal, and 
measure again. If the high resistance is still in take off 
the ground and attach it nearer, and measure again ; if, 
on the contrary, by grounding the first time the high re¬ 
sistance is taken out, the trouble is beyond, and the 
ground must be attached at a more distant point. By 
continuing the measurements the trouble can soon be 
localized between two stations. 

216. How should a ground or dead earth he tested for f 

The method in general use is to call up all the sta¬ 
tions, one after another, and see what ones can be raised. 
If, for instance, a line has twenty stations and the most 
distant one that can be raised is the tenth, the presump¬ 
tion is that the ground is beyond that station. This is 
used where there is only one wire. If there are two or 
more wires the testing office can call the way-offices in 
rotation on No. 2 and direct them to open No. 1. So 
long as the opening is not perceptible at the testing sta¬ 
tion the ground is between the station opening the key 
and the testing station ; but as soon as the opening of 
the key at a station is perceived at the testing station 
the ground is passed and is then beyond the station 
opening. If a galvanometer is used and the normal re¬ 
sistance of the line is known, the distance of the ground 
from the testing station can usually be calculated from 
the measured resistance with the fault in. A dead 
ground is very often caused by lightning burning out 
the paper between the plates or fusing the points of a 
lightning-arrester. On a very short line having many 
stations or instruments, such as a stock-printer line, the 


238 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

quickest plan to locate a ground, is to go from station 
to station. The instruments on the battery side of the 
ground will be observed to work stronger than usual, 
while those beyond the ground will work much weaker 
or not at all. 

217. How does an escape manifest itself, and how is it to be 
tested for i 

An escape is manifested much in the same manner as 
a ground, but its effects are not so pronounced. Stations 
on different sides of an escape, under ordinary condi¬ 
tions have to adjust high to work with each other. It is 
sometimes found advisable to take off the battery from 
one end of the line, and let the magnetism in the relay 
at the receiving end be produced entirely by the influ¬ 
ence of the battery of the sending end: because even 
though a portion of the current from that battery is lost 
at the escape, the portion which does arrive at the re¬ 
ceiving station beyond the escape is necessarily affected 
by the key of the sender, since whenever that key is 
opened all the current is taken from the line. When 
this is done, however, the receiver must not break, as if 
he did it would not be noticed by the sender, the circuit 
being, in any event, partially completed by the escape. 

Figure 85 represents a line with a main battery, E, at 



i 

_i_s£] 


Fig. 85. 

each terminal station, and a fault, consisting of an es¬ 
cape, F, between the two stations B and C ; the terminal 
stations are indicated by the letters A and I). 

To test for this escape the stations of the faulty wire 
must be called up, one after another, either by means of 
a second wire or by the faulty wire itself, and told to 

open key for a minute or so. When the stations bevond 

«/ 








CIRCUIT FAULTS AND THEIR LOCALIZATION. 239 


the escape open a current will be still on the line from 
the testing station to the escape, and will affect the relay 
of the testei ; but as soon as the first station on the test¬ 
ing-office side of the escape opens the current will cease 
and the tester’s relay will fall back. Thus, in the figure, 
supposing A to be the testing station, when C opens key 
there is still a current on the line from the battery E 
through the escape to ground ; but when B opens there 
is no current, showing the escape to be between B and C. 

2IS. How is a cross or contact between two wires to be local¬ 
ized i 

AY hen a cross occurs between two wires it is obvious 
that the two wires will be reduced to one, if one of them 
is opened on both sides of the cross, or if one is opened 
on one side of the cross and the other on the other side 
of the cross. Therefore to test for a cross, say between 
two wires, No. 1 and No. 2, the most distant station that 
can be raised must be called up and instructed to open 
one wire—No. 1, for example—and make dots on the 
other. The testing office will open No. 2, and if the dots 
of the distant station come on No. 1 at the testing sta¬ 
tion the wires are obviously crossed. Now instruct the 
distant station to leave No. 1 open; then call up the 
next distant station, direct it to open No. 1 and send 
dots on No. 2, opening No. 2 at your own station. If 
the cross is still between the testing office and the dis¬ 
tant station the dots will still come on No. 1 ; but if the 
cross is between the station now sending dots and the 
preceding one both wires will now be open at the test¬ 
ing station. The cross is thus readily located. The test¬ 
ing operator or circuit manager must call up and test 
with station after station in regular succession until the 
cross is located. 

219. How must an intermittent ground or cross be tested 
fori 

The only reliable way to test for and locate an inter¬ 
mittent ground is to cross-connect the faulty wire with 
a perfect one and wait until the next time the fault 


240 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

shows, observing then whether it is transferred to the 
second wire with the cross-connected section of line, the 
whole process being in every respect similar to that of 
testing for an intermittent disconnection described in 
question 214. 

The same remarks apply generally to intermittent 
troubles of any character. 

220. How does a weather-cross affect telegraph lines , and 
hoic and when must it be tested for t 

A so-called weatlier-cross shows a similar effect on a 
line of telegraph to that caused by a cross, but in a much 
less degree. It must be tested for in the same way, and 
the testing must be done while the wet weather contin¬ 
ues, as it is only then that such a fault is sufficiently 
apparent to be tested for. 

221. When a defective ground connection is suspected how 
man it b e tested for and discovered t 

When such a fault is suspected it may often be found 
by searching, without testing at all. If it cannot be 
readily found or proved to exist by search, it can be 
tested for by several methods. The first is: If more 
than two lines run to the same earth, first take off all 
the lines except two, then open one of these two and 
put a considerable battery on the other. If the ground 
is very defective a large share of the current will leak 
past it and make itself manifest to the taste at the end 
of the opened wire. A second way is given by Haskins, 
and is as follows: ‘‘Connect a wire to the suspected 
ground wire between the battery terminal and ground, 
or, if you have no battery, to the ground-wire between 
the last instrument and the ground; connect the other 
end of the wire to a galvanometer, connecting the other 
post of your galvanometer to a good earth. If the 
ground is really defective the current will divide where 
the second wire is attached and will go to ground through 
the galvanometer, deflecting the needle.” Haskins also 
gives the following method of measuring the resistance 
of the defective ground : Measure any two lines to earth 


CIRCUIT FAULTS AND THEIR LOCALIZATION. 241 


through the suspected wire, then disconnect the two 
wires from the ground, connect them in metallic circuit, 
and measure the loop so made. If the sum of the two 
resistances measured to ground exceed the resistance of 
the metallic loop, then the excess, divided by two, will 
give the resistance of the defective ground. 


CHAPTER XVII. 


MULTIPLE TELEGRAPHS. 

222. What is meant by the term multiple telegraph % 

The term embraces all the various methods of simul¬ 
taneously sending two or more communications or mes¬ 
sages, either in the same direction or in opposite direc¬ 
tions, over a single line. It includes the duplex, quad- 
ruplex, the various multiplex methods which have been 
introduced or projected within the last ten years, and 
the harmonic systems of telegraphy, introduced by Var- 
ley, Gray, Lacour, and others. 

223. What is the duplex f 

It is simply an ordinary telegraph, so constructed and 
arranged that two communications may at the same time 
be transmitted intelligently over the same wire. Usage 
has applied the name only to systems wherein the two 
communications are transmitted in opposite directions. 

There are two conditions necessary in duplex tele¬ 
graphy—namely, the relay of either station must not 
respond to its own key, while it must readily respond to 
those currents transmitted by the key at the distant sta¬ 
tion, and the currents so coming in at either end from 
the distant station must always have an uninterrupted 
path to the ground. Many inventions have been pro¬ 
duced in duplex telegraphy, but the greater number of 
those in use at the present time operate on the differ¬ 
ential principle, in which the outgoing current divides, 
one part passing through one coil of a differential relay 
to ground through a rheostat, and operating to hold the 
armature still, the other part going through the other 

242 


MULTIPLE TELEGRAPHS. 


243 


coil of the relay to the line to operate the relay at the 
distant station. A differential relay is one which is 
wound with two separate coils in different directions. 
The effect when a current is passed through it is that the 
current from the home battery is equal in both coils, and, 
they being wound in different and opposite* directions, 
the magnetic effect caused by the current in one direc¬ 
tion in the relay will be neutralized by the current in the 
other direction, and so the effect of the outgoing current 
will be nothing ; but when the current in the coil leading 
to line is reinforced by a current from the distant sta¬ 
tion, it overbalances the current in the other coil and 
gives the signal. The only other popular and much- 
used system of duplex is what is known as the bridge 
duplex. In it the receiving instrument is placed in the 
cross wire of a Wheatstone bridge, and the connections 
are arranged in accordance with that well known prin¬ 
ciple. The success of both the differential and bridge 
duplexes is due to the improvements made by Mr. Joseph 
B. Stearns. 

224. Give a brief history of the duplex , naming its successive 
improvers and inventors. 

The first to broach the idea of using one wire for the 
simultaneous transmission of two messages was Mr. 
Moses G. Farmer about 1852. Dr. Gintl, director of the 
Austrian State Telegraphs, was, however, in 1853 inventor 
of a practical duplex system, which was the parent stem 
of the present differential systems. He used a differen¬ 
tial relay, of which one coil was traversed by the line 
current, and the other by the current of a local equating 
battery of opposite polarity, the combined effect being 
to hold the armature of the home relay still, and thus 
subject to the action of the current coming from the dis¬ 
tant station. It was very rudimentary, and was in rapid 
succession followed by the duplex systems and improve¬ 
ments of Frischen in 1854 ; Gintl, in a chemical duplex, 
which was practically operated in 1854 between A ienna 
and Linz; Nystrom, of Sweden, in 1856, whose princi- 


244 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


pal improvement was to maintain the connection between 
the line and earth always unbroken by means of a cir¬ 
cuit-preserving key ; Mr. W. H. Preece, of England, in 
1855 and 1856 ; Siemens and Halske’s two-relay method ; 
Zur Nedden in 1855, and Farmer in 1858. All of these 
different improvements, however, fell flat, chiefly because 
the time for them had not arrived, and the science of 
telegraphy was not developed to such an extent as to 
require a satisfactory system of duplex telegraphy. 
Hence all these methods were looked upon merely as 
electrical curiosities. In 1863 the interest in this branch 
of telegraphy seemed to revive, and Maron, a Prussian 
telegraph inspector, effected another improvement by 
which the receiving instrument was placed where it 
would not be acted upon by outgoing currents. Fris- 
clien also, in 1863, improved his former method. In 1868 
Mr. Joseph B. Stearns, of Boston, commenced a series 
of experiments with the duplex of Siemens and Halske, 
and was soon so successful that duplex telegraphy, 
which had now become a necessity, was roused from the 
torpor 'which had hitherto crippled it, and was rapidly 
brought into general use. He applied a transmitter in a 
local circuit instead of the old key, and caused it to 
make the contact of the battery with the line before the 
interruption of the contact between the line and the 
ground. He made this transmitter act also as a sounder, 
so that the American operator, accustomed to hear his 
own sending, could be thus accommodated. He subse¬ 
quently connected a condenser to the rheostat, forming an 
artificial line, and thus balanced the static charge which 
came from the line when the line was changed from bat¬ 
tery to ground. Mr. Stearns also introduced his trans¬ 
mitter and condenser into the bridge system, where the 
receiving instrument is placed in the cross-wire of a sys¬ 
tem of circuits and resistances, arranged at each station 
on the plan of the well-known Wheatstone bridge. The 
receiving instrument is thus placed beyond the range of 
electrical impulses originating at its own station, while 


MULTIPLE TELEGRAPHS. 


245 


free to respond to those caused by the distant station. 
This is widely used and known universally as the bridge 
duplex. The success of Mr. Stearns spurred up many 
inventors, and duplex telegraphs, each having features 
more or less meritorious, were brought out by the follow¬ 
ing well-known electricians: Gerritt Smith ; Yaes, of 
Rotterdam ; G. K. W inter, of India ; George D’lnfre- 
ville, J. C. TV ilson, C. H. Haskins, T. A. Edison, and 
others. Duplex telegraphs are still being produced, 
although the quadruplex has greatly diminished their 
importance. 

225. Give a short description of the entire principle of the 
Stearns differential duplex. 

The differential relay, as heretofore explained, is a re¬ 
lay the magnets of which are wound with two separate 
wires of equal length and size, and consequently of equal 
resistance Such a relay is employed ; and tlie wire from 
the main battery, which is controlled by the transmitter, 
is connected with the leading-in wire of one coil, and 
with the leading-out wire of the other coil, so that when 
by the action of the transmitter the battery is thrown 
on to the main wire of the relay, the current circulates 
round the soft-iron core in both directions at once, and 
the magnetic result in the core is consequently nothing, 
so long as the home current only is employed. One of 
the wires leading from this relay is now connected to 
the line-wire, and the outer end of the other is con¬ 
nected to a rheostat or resistance-coil of approximately 
the same resistance as the line. It will be observed, 
therefore, that the respective differential circuits of the 
relay are both extended, the one through a long line 
to earth, the other through a resistance to earth. It 
was one of the old difficulties that when the contact of 
the line to earth was interrupted a momentary break 
occurred before contact with the battery was made; Mr. 
Stearns so arranged his transmitter that the contact of 
the battery was made before that of the line with the 
earth was broken, much as Nystrum had done in 1856. 


246 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


The transmitter is operated by a local circuit and an 
ordinary Morse key, and its entire office is to alternately 
put the line to battery and ground.* 

It was found that when the battery was connected to 
the line, the line became statically charged, and when it 
was put to earth this charge returned through the relay, 
causing it to give a “kick.” Stearns saw that all the 
conditions of a line of telegraph were not fulfilled by his 
balancing resistance-coil, and he accordingly devised the 
attachment of a condenser around the rheostat or resist¬ 
ance-coil which formed the artificial or balancing line. 
This added the missing feature, electro-static capacity, 
with the result that when the line was charged the con¬ 
denser connected to the artificial line was also charged, 
and when the line discharged through one wire of the 
relay the condenser discharged through the opposite 

wire, thus balanc- 



LINE 


->-B 


ing the forces and 
neutralizing 


1? 




H 


r t 






dL 


K 


GROUND 


Fig. 86. 


the 

“kick.” 

Figure 86 is a 
theoretical dia¬ 
gram of one sta¬ 
tion, arranged for 
duplex transmis¬ 
sion, with the local 
connections omit¬ 
ted. T is the trans¬ 


mitter, operated by a local battery and key, K, and con¬ 
necting with the relay, II; this is wound differentially, 
the wire leading from the transmitter dividing at the 
point H, one division traversing the relay in one direc¬ 
tion and leading to line B, and the other passing 
through the relay in the opposite direction, and through 
a wire, A, and rheostat, X, to ground. The transmitter is 
also grounded by a wire extending from its lever to the 


* The invention of the transmitter is now ascribed to Farmer. 






































MULTIPLE TELEGRAPHS. 


247 


•ground-wire. Tlie condenser, I, is shown connected as a 
shunt to the rheostat, and is united on one side to the 
wire A at a point between the relay and rheostat, and 
on the other side to earth. 

The differential relay, being, as we have described, ir¬ 
responsive to the impulses of the transmitter at its own 
station, yields readily to those sent from the distant sta¬ 
tion, because the currents passing through the line-coil of 
the relay are reinforced by the current coming from the 
distant point, and thereby predominate over that part of 
the current which passes through the artificial line; 
magnetism in the relay-core ensues, and the signals are 
produced. 

226 . Give a general description of the bridge duplex. 

The bridge duplex is simply an arrangement of cir¬ 
cuits, in which the receiving relay is placed in the cross¬ 
wire of a Wheatstone bridge or balance. It is well 
known that the Wheatstone bridge is usually repre¬ 
sented by a diamond-shaped parallelogram, with two of 
the opposite corners connected respectively to the two 
o})posite poles of a battery; the other two opposite 
corners being connected by a cross-wire having a gal¬ 
vanometer in circuit. In such an arrangement of circuits 
no current passes through the cross-wire, provided the 
resistances of the opposite circuits on each side are 
eitlier equal, or are in the same ratio, one to the other. 
It is, of course, immaterial what form the arrangement 
of the circuits really is in, if the connections are sub¬ 
stantially as indicated here. 

The foregoing principle is utilized in the bridge du¬ 
plex. Figure 87 shows in diagram the theoretical ar¬ 
rangement of the bridge duplex. The battery is con¬ 
nected through the transmitter, K (which in practice is 
similar to that of the differential duplex), to the point, 
H, where the circuits diverge to form the arms of the 
bridge; between this point and the cross-wire, on each 
side, are placed adjustable resistances, A and B, thus 
forming the first two arms of the bridge; the line L to 


248 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

the distant station, and there to earth, is the third arm, 
while a rheostat, R, looped by a condenser, C, is the 
fourth arm. The relay, M, is placed in the cross or bridge 
wire. Y and W are small resistances placed in the cir¬ 
cuit to prevent any short-circuiting of the battery, and 
also to avoid variation of resistance when the line is 
changed from battery to ground, or vice versa. 



Fig. 87. 


The four resistances are adjusted to a suitable ratio, 
so that the relay does not respond at all to the outgoing 
current, while it must respond to the incoming current, 
since a certain portion of that current must necessarily 
pass through it to earth. The condenser in this system 
is adopted for the same reason as in the differential sys¬ 
tem—namely, to counteract the effect of the electro-static 
discharge from the line by a similar one in the opposite 
direction from the condenser. 

The great advantage of the bridge is that it can be 
readily used with any character of apparatus, from a 
relay to a Thomson galvanometer. It is also less likely 
to suffer injury from lightning than is the differential. 

Ordinarily for long circuits the differential is to be 















































MULTIPLE TELEGRAPHS. 


249 


piefened, because with, a given amount of battery a 
stronger working current and a greater magnetic force is 
developed in the receiving instrument. 

227 . 11 hat has been done towards duplicate transmission in 
the same direction i 

The first attempts in this direction were made in 1855 
by Dr. J. B. Stark, of \ ienna, and by Siemens, of Ger- 
many; these were shortly after succeeded by Kramer, 
and subsequently by several others. None of these sys¬ 
tems was ever brought to practical application, although 
all were most ingenious and beautiful. 

A description of the method of Stark will suffice, as 
showing the general tendency of all. Two keys are, of 
course, required at the sending station, and two receiving 
relays at the receiving station. Four conditions are 
therefore to be provided for—namely, 1st, when No. 1 
key is closed and the other open; 2d, both keys closed ; 
3d, No. 2 key open and No. 1 closed ; and, 4tli, both keys 
open. Dr. Stark accomplished this by sending with key 
No. 1 a comparatively weak current, and with No. 2 key 
a stronger current, while when both keys were closed 
the combined currents were sent; finally, when both 
keys were open no current was on the line. He ar¬ 
ranged at the receiving station two relays, so constructed 
that when the weaker current was sent one relay would 
respond, and when the key sending the stronger current 
was depressed the other relay would respond; while 
when both keys were operated both relays would re¬ 
spond. This was effected by adjusting the relay work¬ 
ing with the strong current with a retracting spring of 
high tension, so that its armature would not move with 
the weaker current. When, however, the other key was 
depressed, the armature of the relay moved, and not 
only closed the circuit of its own register or sounder, 
but also closed the circuit of another or auxiliary bat¬ 
tery, causing a current to circulate round the coils of the 
first relay which is differential but in an opposite direc¬ 
tion to that of the line current; the armature of that 


250 ELECTRICITY, MAGNETISM, AND TELEGRAPH Y r . 


relay is thus held quiescent. When both keys are ope¬ 
rated the current passing through the coils of the first 
relay, or that responding to the weak current, is strong 
enough to overcome the local current in its other coil, 
and it also responds. 

Serious difficulties developed themselves in this system, 
as in others of the same class; and not until the practi¬ 
cal introduction of the Stearns improvements on the du¬ 
plex was this idea made thoroughly practical. 

228 . What is the quadruplex f 

The quadruplex is the name given to the apparatus 
and method whereby four messages may be transmitted 
upon one wire simultaneously, two in one direction and 
two in the other. 

229 . How far back does the idea of a quadruplex date, and 
to whom is its first conception due f 

It dates back to 1855, when Stark, while experiment¬ 
ing on the problem of double transmission in the same 
direction, saw that upon the successful solution of that 
problem depended that of the greater problem of quad¬ 
ruplex telegraphy. His description of his proposed 
method of simultaneous transmission in the same direc¬ 
tion concludes with the following memorable words: 
“With the method of double transmission in the same 
direction we may also combine that of counter or oppo¬ 
site transmission ; and hence arises the possibility of 
simultaneously exchanging four messages upon one wire 
between two stations, which will, however, hardly find 
any application in practice.” Dr. J. Bossclia, Jr., of 
Leyden, also, about the same time foresaw the ulti¬ 
mate result of a successful system of double trans¬ 
mission in the same direction, and in a paper read before 
the Royal Academy of Sciences in Holland, in 1855, 
after describing his own method for the accomplishment 
of that feat, he proceeded to outline a method of achiev¬ 
ing the greater result. He simply proposed to add to 
his own system the duplex of Siemens and Halske, or 
of Frischen. It is very evident, therefore, that both of 


251 


MULTIPLE TELEGKAPHS. 

these inventors recognized the fact that quadruplex tele¬ 
graphy depended entirely upon a successful system for 
double transmission in the same direction. 

230 . What is the origin and principle of the American quad - 
ruplex i 

It originated in experiments made in 1874 by Thomas 
A. Edison, in association with George B. Prescott, with a 
view of improving the Stearns duplex. While engaged 
in this work Mr. Edison devised a new method of double 
transmission in the same direction, which was more 
practical than any of its predecessors, and at the same 
time differed essentially from them. His method was, 
like the discovery of America, simx>le enough when 
known, and consisted in combining the system of tele¬ 
graphy known as the double-current system, wherein 
the telegraphic signals are transmitted by rapidly re¬ 
versing the poles of a battery which is always kept on 
the line, so that the current is constantly alternating in 
direction from positive to negative, and vice versa , with 
the single-current system, wherein transmission is ac¬ 
complished by breaking and closing of the circuit, but 
in this case the current is simply made to increase and 
decrease. Thus two distinct qualities of electricity, 
direction or polarity, and strength, are utilized, and an 
entirely new method of double transmission in the same 
direction was the result. As foreseen by Stark and 
Bosscha, it was now an easy matter to apply to this 
new method the Stearns duplex, or indeed any other 
practical duplex ; which was accordingly done, giving 
to the world the far-famed quadruplex. 

It was ascertained by practical experiment that the 
bridge duplex was better adapted to the conditions 
necessary for success than the differential, and the 
bridge was therefore employed with the earlier com¬ 
bined systems. In practice two transmitting instru¬ 
ments were set up at each end of the line, both worked 
by an ordinary Morse key, opening and closing a local 
battery circuit. One transmitter, the one nearer to the 


252 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


line, operated simply as a pole-changer without regard 
to the strength of battery used. The other operated, 
when depressed, to add to the ordinary battery about 
three times as many cells as it would usually have, so as 
to increase the strength of current correspondingly, irre¬ 
spective of the polarity. A certain amount of battery 
was to be always in circuit. These transmitters were 
placed in the circuit of the wire leading from the battery 
to the bridge. In the cross-wire of the bridge, at each 
end of the line, were placed two relays : one a polarized 
relay, responding only to the sending of transmitter lS r o. 
1 at the opposite end, or the pole changer ; and the other 
a relay with a neutral or nou-magnetic armature, which 
responded only to the sending of the transmitter No. 2, 
which increased or decreased the battery. By the use 
of this apparatus it was made possible to send two 
messages from each terminal station at the same time, 
and consequently to receive at both stations an equal 
number. An old annoyance, however, showed itself here. 
The moment of change of polarity, when the polarized 
relay was being operated, would alfect the neutral relay, 
causing it, if occurring at the same time that the neutral 
armature was attracted, to make a false break. To 
remedy this defect Edison caused the armature-lever 
of his neutral relay to make contact on its back limit- 
stop, closing a local circuit which included an electro¬ 
magnet. This electro-magnet in turn closes the sounder 
circuit by making contact on its back stop. By thus 
interposing a local circuit the interval of non-magne¬ 
tism was made too brief to affect the sounder. He 
also incorporated an additional electro-magnet and a 
condenser, looping a rheostat placed in the bridge- 
wire, to overcome the effects of the static discharge 
upon the neutral relay. These devices were, how¬ 
ever, cumbersome, and not always effectual, and, 
though the quadruplex was at this time a tolerable 
success, it left much room for improvement by subse¬ 
quent inventors. 


MULTIPLE TELEGRAPHS. 


253 


231 . What changes and improvements have been made in the 
quadruplex since its introduction t 

The changes in the working arrangement of the quad¬ 
ruplex have been numerous and important; and although 
many of them have been the result of careful and pains¬ 
taking thought and exhaustive experiment, curiously 
enough, at the present time, after a fair trial of the nu¬ 
merous modifications, the entire system in its essential 
features is much the same as when first made public. 

The improvements referred to were, of course, made 
with a view of simplifying the apparatus and arrange¬ 
ment, and of obviating certain faults which had showed 
themselves. In place of the bridge it was found possi¬ 
ble to substitute the differential-circuit arrangement. A 
compact double-current transmitter was devised, and 
certain receiving instruments were brought into use, 
which, while comprising features of great novelty and 
ingenuity, unfortunately introduced rlie element of com¬ 
plication. The new double-current transmitters have 
been made extremely simple, and yet capable of the 
most accurate adjustments, so that the current of one 
polarity does not cease till that of the opposite polarity 
commences to flow, while at the same time the time that 
the battery is placed on short circuit is reduced to an 
infinitesimal period. 

The receiving relays were, as already indicated, some¬ 
what complicated, a polarized relay replacing the neu¬ 
tral relay of Edison. This was so arranged with contact- 
levers that at all times when the entire force of the 
batteries was on the line its local circuit was opened, 
because the armature was either drawn to its full ex¬ 
tent in one direction or the other, in either case open¬ 
ing the local circuit. When, however, the battery cur¬ 
rent on the line was decreased or withdrawn by the de¬ 
pression of the proper key, the armature, not being so 
forcibly attracted, would stay in the centre, being held 
there by its contact-levers, at the same time closing 
the sounder circuit. The other relay was, of course, 


254 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


also polarized, and responded to the movements of 
the double-current transmitter only, closing* its local 
sounder circuit only when its armature was drawn to 
one particular side by a current of definite direction, 
whether that current be strong or weak. Thus both re¬ 
lays were by this plan polarized, one closing its local 
circuit when drawn to one side and opening it when 
drawn to the other side, and the other closing its cir¬ 
cuit only when a weak current was on the line, and 
breaking it the moment a strong current was trans¬ 
mitted. The principal defect in the original quadru- 
plex—namely, that of allowing the neutral relay to make 
a false break at the moment when the direction of the 
current changed—was thus overcome. Subsequently it 
was ascertained that a small neutral relay with short 
cores was capable of being reversed with sufficient 
rapidity to answer every requirement, and such a relay 
was then made to replace the double-tongued polarized 
relay, thus bringing the quadruplex back almost to its 
original form. 

The usual arrangement of the quadruplex as now 
operated includes the neutral relay, and has a con¬ 
denser between the main and artificial line. The differ¬ 
ential system is also preserved. 

In New York dynamo-electric currents are used ; and 
in conjunction with them it has been found necessary 
to employ an entirely novel key system, the ordinary 
quadruplex key system not being suitable. 

Probably the longest circuit in the world working 
quadruplex all the way through is that between New 
York and North Sydney, C. B., via Worcester, Port¬ 
land, and Bangor; a repeater being in circuit at the 
latter place, the entire distance being about twelve hun¬ 
dred miles, and the line built of No. 4 galvanized iron 
wire. 

232 . What is the electro-harmonic system of telegraphy i 

It is a telegraphic system based upon the facts that 
musical tones produced by the vibration of an electro- 


MULTIPLE TELEGRAPHS. 


255 


tome or circuit-breaker may be transmitted through a 
telegraphic circuit, and reproduced at the other end of 
the line in tones of like pitch, by the vibrations of suit¬ 
able armatures ; and that by employing a set of circuit 
interrupters or changers, each acting by rapid vibration 
to produce a distinct musical tone of a pitch different 
from the others, and transmitting the said tones, suc¬ 
cessively or simultaneously, over a single circuit com¬ 
mon to all the circuit-breakers, and through a series of 
electro-magnets fitted, instead of armatures, with steel 
ribbons rigidly fixed at one end and provided with 
turning-screws at the other, so as to give them the 
proper tension, each of these ribbons being tuned to give 
out the same note as its corresponding circuit-inter¬ 
rupters, each receiver will analyze the tones transmitted 
through it, pick out its own, and allow the others to 
pass without interference or interruption to their re¬ 
spective receivers. 

The method of applying this system to telegraphy is 
well explained in an article prepared under the super¬ 
vision of Mr. Gray (who has been the chief inventor in 
this application of electricity) for the New York Review 
of the Telegraph and Telephone , and also in a lecture 
delivered before the New York Electrical Society, April 
6, 1883, and subsequently published in the New York 
Operator. 

The following description is chiefly drawn from these 
sources: 

A battery, P 15 P 2 , P 3 , P 4 , Figure 88, united on one side 
to the ground, sends in line L an electric current which, 
at the receiving station, crosses seriatim a certain num¬ 
ber of electro-magnets—four, for example, E 1? E 2 , E s , E 4 . 
Before these latter are placed the reeds B n B 2 , B 3 , B 4 , 
and, under the influence of the variations of the intensity 
of the current, each electro-magnet puts in vibration, 
like the diaphragm of the telephone, a corresponding 
reed. Further, the four reeds, fixed permanently at one 
of their extremities, are regulated in such a way as to 


256 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

give in vibrating four entirely distinct tones; conse¬ 
quently each of them is only affected by the vibrations 
of the current when these variations are in accord with 
the number of vibrations which correspond to it. 

On the other side the battery of the sender is divided 
into four groups, and upon each of these groups is dis¬ 
posed a derived circuit, including a vibrating reed and a 



key for making and breaking the contact. There are 
thus four vibrating reeds, vibrators V„ V 2 , V 3 , V 4 , and 
four contacts, C„ C 2 , C 3 , C 4 . Each time that one of the 
vibrators touches its contact the circuit from the corre¬ 
sponding battery is shut off and the current is dimin¬ 
ished ; when the circuit is again cut on the current re¬ 
sumes its first intensity, but the vibrators set in action, 
each by a special magneto-electric system, are constantly 
driven by a determinate vibratory movement, and the 
number of vibrations of each of them is the same as that 
of one of the reeds of the receiving apparatus ; that is to 
say, that V, will have a number of vibrations equal to 
that of tlie tone which gives 13,, V 2 the number of vibra¬ 
tions corresponding to the tones of B 2 , etc. Each vibra- 

























































multiple telegraphy. 257 

tor will determine then in tlie current very rapid vibra¬ 
tions, and will produce a series of electric waves in 
relation with the number of vibrations which it effects. 
All the vibrators being in action at the same time, there 
will pass, consequently,‘in the line four series of distinct 
electric waves ; and each of these series of waves find¬ 
ing at the receiving station a reed in harmony with it, 
under its influence all the reeds, B„ B„, B s , and B 4 , will 
enter into vibrations. 

If now one of the vibrators is stopped the series of 
electric waves which correspond with it would be sup¬ 
pressed, and the corresponding reed ceases to vibrate. 
If two. three, or four of the vibrators are stopped the 
arrest of two, three, or four of the reeds will be effected. 
These arrests will be heard at the receiving station ; and, 
by making short and long stops, a sort of Morse alpha¬ 
bet can be arranged to transmit simultaneously four 
different despatches. 

What we have said represents, in short, the harmonic 
system of transmission invented by Mr. Gray; but it 
is evident that in practice special arrangements must 
necessarily be taken to assure good results. We wish 
now to indicate these arrangements, after having de¬ 
scribed in detail the different apparatus employed. 

We will describe, in the first place, the receiving ap¬ 
paratus, and will indicate how, in the place of producing 
signals by means of stops in the sound of the receivers, 
these stops are transformed into electric contacts sus¬ 
ceptible of producing ordinary electrical signals. 

The receiver, with its local sounder, battery, and con¬ 
nections, is represented in Figure 89. To the left of the 
vibrating end of the reed is a supporting jriece holding a 
small bent lever, called a rider, which is nearly balanced 
at A, and having its bent end resting lightly on the reed 
at E. The local circuit, starting from the batteiy, B, 
travels through the sounder, C, enters the reed at I), the 
rider through the contact-points. E, and the wire again at 
A, thence back to the other pole of battery B. When 


258 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

9 

tlie reecl is in vibration the local circuit is virtually 
broken at E by the rider being kicked off, and so much 
resistance put in at that point by reason of the very im¬ 
perfect contact. The instant the reed comes to rest the 
adjusting spring pulls the rider down and closes the 
local circuit. 

Consequently, when at the transmitting station all the 
vibrators act upon the battery, all the sounder circuits 
are opened. If, on the contrary, one of the vibrators 




Fig. 89. 


stops, the sounder circuit of the corresponding reed is 
closed. The arrest of a vibrator then acts on its corre¬ 
sponding sounder as that of a Morse key would act, in¬ 
serted with it, in the circuit of a battery. 

The vibrator is represented by Figure 90. The electro¬ 
magnets, A and B, have respectively one and thirty ohms 
resistance. The current of the battery, passing through 
the coils of the two electro-magnets, magnetizes them 
simultaneously, but on account of the greater number of 
convolutions the electro-magnet A is the stronger. It 
thus attracts the steel tongue which hangs from a fixed 
point between the magnet-cores. This tongue then 
makes contact by means of the spring I) with the point 
C, establishing a shunt circuit round the magnet A, 


































































multiple telegraphy. 


259 


round winch the current may now pass. The electro¬ 
magnet B becomes consequently stronger, and in its 
turn attracts the tongue until the spring F makes con¬ 
tact with the screw E. The contact 1) being broken 
anew, the electro magnet A again attracts the steel 
tongue,. and thus . rapid motion is maintained. The 
tongue is then maintained in vibration, which is regu- 


Fig. 90. 



lated according to its fundamental tone. The contact F 
represents one of the contacts indicated in Figure 88 by 
the letters C„ C a , C 3 , and C 4 . 

In the disposition of Figure 88, when the vibrator is 
in action by the operation of the battery which corre¬ 
sponds to it, it enfeebles this part of the battery in a 
proportion of about sixty per cent. When the vibrator 
is stopped its group of battery resumes all its force, 
and will tend to increase the intensity of the current in 
the line. With four vibrators, several among them be¬ 
ing liable to be stopped at the same time, the changes of 






































































































































































































260 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

intensity would be very considerable and would injure 
the results derived from the system. In order that this 
latter effect may not take place it is necessary, at the 
same time that a vibrator be stopped, to suppress from 
the circuit the sixty per cent, of the group of the corre¬ 
sponding battery, in order to produce on the general cur¬ 
rent the same effect as the vibrator when it was in action. 
To attain this result Mr. Gray, instead of stopping the 
vibrator by opening the local circuit, which is the idea 



77t 


Fig. 91. 


which presents itself naturally to the mind, produces 
this arrest by the aid of a special disposition called the 
transmitter, and represented by Figure 91. The princi¬ 
pal part of this disposition is a lever of brass, A. It is 
terminated at one end in the form of a T. A spring, R, 
insulated by a piece of ebonite, is placed on the upper 
part of a lever, and a second spring, r, is in communica¬ 
tion with the lower part. These two springs impinge at 
their extremities upon a branch of the T when they are 
not removed from it by one or other of the regulating 
faces, B and S. An electro-magnet, moved by the local 
battery, p , and a key, 7c, is placed above the armature of 
the lever. 













































MULTIPLE TELEGRAPHY. 


261 


One of the extremities of the main battery is in com¬ 
munication with the axis, 0, of the lever, the other with 
the vibrator and also with the adjoining instrument; 
the spring R is united to the line; the face S communi¬ 
cates with the contact, C, to the vibrator. Finally, face B 
is in relation with a point of the battery dividing this 
battery into two parts, which should be in ratio of sixty 
to forty. 

In the position indicated by the figure the negative 
pole of the battery communicates with the line by the 
lever, A, and the spring, R ; the positive pole communi¬ 
cates with the adjoining instrument. The contact, C, is 
thus in relation with the negative pole of the battery. 

Then happens the arrangement shown in Figure 88, 
and the movements of the vibrating tongue act upon the 
battery to produce an undulatory current and to weak¬ 
en this group about sixty per cent. It is so when the 
key, k, remains open ; but when this key is closed the 
lever is attracted by the magnet, the spring r abandons 
the face S, and the spring R is supported upon the con¬ 
tact B, but ceases to touch the T of the lever. 

The portion of the battery to the left of B is then ex¬ 
cluded from the circuit, and it is only the portion at the 
right, or forty per cent, of the battery, which sends its 
current one way in the line by B and R, and the other 
way in the other adjoining transmitters by m. The sum 
total of the current has not changed, and the closing of 
Tt lias the effect simply of suppressing the series of elec¬ 
trical waves corresponding to the vibrator, V, and conse¬ 
quently of stopping the corresponding vibrating reed. 

It might be asked why the depression of the lever, 
A, is accomplished by the aid of a local circuit instead 
of being depressed directly. The reason for this is in 
the fact that the pressure of the hand would be very 
unsteady and the contacts would be irregular ; with the 
attraction of an electro-magnet, however, on the other 
hand, the force producing the depression is always the 
same. If now the instruments are connected up in the 


262 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


manner described, we have the general plan sliown in 
Figure 92. This part constitutes the Harmonic system, 

properly so called. 
It perm its the trans¬ 
mission of four de¬ 
spatches simulta¬ 
neously in a sin¬ 
gle direction—that 
is to say, from the 
transmitting sta¬ 
tion to the receiv¬ 
ing station ; but it 
is necessary that 
the employees at 
the receiving sta¬ 
tion be able to 
communicate with 
those at the trans¬ 
mitting station, in 
order to be able to 
respond to the calls- 
or to make correc¬ 
tions. 

As shown in Fig¬ 
ure 92, a differ¬ 
ential relay is used 
at the sending sta¬ 
tion and a plain 
relay at the receiv¬ 
ing station, each 
having a condenser 
in a shunt circuit 
around it to permit 
the vibrations to 
pass without be¬ 
ing retarded or interfered with by the charging and dis¬ 
charging of the magnets. The compound transmitter at 
the receiving station will need some explanation. The 



aui'j-utvjt? 





















































































MULTIPLE TELEGRAPHY. 


203 


two springs, S s, are both insulated from the lever by 
ebonite and connected together; the upper branch of 
the T is insulated from the spring S at E, and the lower 
spring, is insulated from the point c at e. The upper 
point C is connected directly to ground. R and R/ are 
adjustable resistances. R is the artificial circuit or 
equating resistance. When all are sending from the 
sending station, the current, after passing through the 
tone and simple relays, reaches ground through R'; 
that is to say, the circuit in its normal state has the 
artificial resistance of R' constantly interposed. When 
it is necessary to break, which is done by operating the 
compound transmitter by one of the keys, the resis¬ 
tance R is thrown out of circuit and the current on 
the line is augmented in proportion to the amount of 
resistance contained in R 7 , which has been thrown from 
the circuit. The increased line current then divides at 
D, part of it going through the relays and the transmit¬ 
ter to ground from the point C, and part of it through 
R, the transmitter, and the point C. The resistance R is 
adjusted to shunt off part of the increased line current, 
and so maintain an unvarying strength through the re¬ 
lays regardless of the position of the transmitter lever. 
This decrease of resistance, however, throws the line out 
of balance and operates the relay N at the sending sta¬ 
tion, where the signals transmitted by any one of the 
breaking keys are reproduced. We thus have a sixth 
transmission in a direction opposite to the other five, 
and in practice the sixth side is used for breaking and 
other service work. As will be seen by reference to 
Figure 10, each receiving operator has a breaking key, 
and all of these work the compound transmitter, which 
operates the relay N at the distant station. This relay 
in turn controls as manv sounders in its local circuit as 

t j 

there are sending operators. The sections are numbered 
in regular order from one to five at each end. When, 
for instance, No. 2 receiver wishes to break No. 2 sender, 
he simply makes the figure 2 on his key, which is heard 


264 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


on all tlie sounders at the other end, but only No. 2 
sender stops work to get his break. Two or three hours’ 
practice enables any operator to become accustomed to 
this method. 

Condensers are placed in derived circuit upon each 
resistance. They have the effect of compensating the 
extra currents which are produced in the coils of the re¬ 
sistance, and which retard the undulatory currents ; in 
fact, they play the same role as in the Ruhmkorff or 
Ritchie induction-coils. 

In Figure 92 the four groups of the battery are repre¬ 
sented as being equal. In practice they are not so. All 
the groups are divided by the line running to the con¬ 
tact surface B, in two parts, which stand to each other in 
the ratio of sixty to forty ; but the absolute value of all 
the groups is not the same. The reason for this is in 
the fact, demonstrated by experience, that four pulsa¬ 
tory currents, produced by the action of four vibrators, 
are not produced with equal facility. The electro¬ 
motive force necessary for their production is not the 
same for all ; hence the necessity for making the groups 
of different value. 

The Harmonic system of Mr. Gray has been experi- 
mented with in this country from the 22d of November, 
1880, to the 22d of January, 1881, upon the lines of the 
Western Union between New York and Boston, over a 
distance of 240 miles. The trial was made under un¬ 
favorable circumstances, for the line employed was in 
the vicinity of other lines upon which nine quadruplex 
circuits were working, and the currents of these instru¬ 
ments created difficulties in the way of induction in the 
neighboring wires, by reason of the employment of 
strong batteries and frequent changing of the poles of 
the battery. In one of the experiments live employees 
have transmitted, in the space of nine hours, 2,124 de¬ 
spatches, or 286 despatches in all per hour, or 47 de¬ 
spatches per operator per hour. Another time four 
employees, chosen among the best, transmitted, in live 


MULTIPLE TELEGRAPHY. 


265 


liours, 1,184 despatches, or 59 per employee per hour. 
After these experiments, the franchises required by a 
company which is occupied with the construction of 
special lines to operate in competition with the exist¬ 
ing telegraph companies in this country, were acquired. 
The Duplex, or W ay Harmonic, which is a modification 
of the system which we have just described, is already 
■employed on several railroads. 

At least live experimenters worked in the line of Har¬ 
monic telegraphy during the years between 1870 and 
1876 inclusive—viz., Varley of London, La Cour of Copen¬ 
hagen, Gray of Chicago, Bell of Boston, and Edison of 
New York. And, although Mr. Varley was the earliest 
in the field, Mr. Gray has done so much to develop Har¬ 
monic telegraphy, and make it not only practicable but 
also practical, that it seems but fair to award him the 
greatest share of the credit A 

* Since the above was written the Harmonic system has successfully 
been operated over the low-resistance compound wire of the Postal Tele¬ 
graph Company between New York and Chicago, a distance of one thousand 
and twenty miles, without the intervention of repeaters. 


CHAPTER XVIII. 


MISCELLANEOUS APPLICATIONS OF ELECTIIICITY—ELEC- 

TKIC LIGHTING. 

233 . To uiiat useful arts, besides telegraphy, has electricity 
been applied % 

It is impossible in a work of this general nature to 
enumerate all the useful applications of electricity; its 
principal applications are, however, the following: elec¬ 
tric lighting, electro-plating, electro-typing, bell-ringing 
and signalling, telephony, medical applications, or thera¬ 
peutics, clocks, blasting, and gas-ligliting. 

234 . What is the electric light , and under what divisions 
may electric lights be classed f 

By the electric light is meant any light produced by 
the action of electricity, and all sncli lights up to the 
present time may be regarded as belonging to the fol¬ 
lowing divisions: arc lights, incandescent lights, and 
semi-incandescent lights. The so-called electric candles 
are, properly speaking, but a special variety of the arc. 

235 . What is the arc light f 

It is the extremely brilliant light produced when the 

two conductors leading from the 
poles of a powerful source of elec¬ 
tricity are brought together so as 
to complete the circuit, and then 
slightly separated. It is, as shown 
in Figures 93 and 94, of curved 
form when produced in the open 
air, by means of horizontal elec¬ 
trodes, and is for that reason originally called an arc. 

The more powerful the source the greater may be the 

length or span of the arc, and the more intense and bril- 

266 





MISCELLANEOUS APPLICATIONS OF ELECTRICITY. 267 

liant tlie light emitted by it. If the two severed ends of 
the circuit are made of carbon, and pointed, the effect is 
materially augmented. The arc is supposed to originate 
in the passage between the electrodes of the self-in¬ 
duced extra current, which attempts to leap from one 
carbon to another, and in doing so volatilizes a small 
amount of carbon. The carbon vapor thus produced has 
a very high resistance, and, while capable of conducting 
the current, becomes heated by its passage, the carbon 
points also growing hot. Numerous small particles of 
carbon are then thrown from one pole of the arc to the 
other, and during their transit become incandescent, 
thus aiding in the illumination. The direction in which 
the particles move is dependent upon the direction of 
the current; that is, from the electrode or conductor 
leading from the positive, to that leading from the nega¬ 
tive pole. 

The positive terminal of an arc light is much hotter 
than the negative, and is consumed much faster. When 
enclosed in a vacuum, the consumption of both elec¬ 
trodes is much less rapid than when the arc is exposed 
to the air. 

For illuminating purposes the electrodes are nearly 
always made of carbon. The color of the luminous arc 
depends on the material of the electrodes ; for example, 
carbon produces a white, copper or silver a green, and 
sodium a blue light. The electricity traverses the arc, 
which is, therefore, a part of the circuit. 

The arc was first produced by Sir Humphry Davy, by 
means of large voltaic batteries, from which the name 
voltaic arc , often applied to it, is derived. 

The following lines are transcribed from the work of 
Professor Silvanus P. Thompson: “ The resistance of 
the arc may vary, according to circumstances, from five- 
tenths of an ohm to nearly one hundred ohms. To pro¬ 
duce an electric light satisfactorily, a minimum electro¬ 
motive force of forty to fifty volts is necessary ; and as 
the current must be at least from five to ten amperes, it 


268 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


is clear that the internal resistance of the battery or 
generator must be kept small. With weaker currents, 
or smaller electro-motive forces, it is impracticable to 
maintain a steady arc. Therefore the internal resis¬ 
tance of the ordinary Daniell or Leclanche batteries is 
too great to admit of their use in producing the electric 
light. A battery of forty to sixty (trove cells will an¬ 
swer the purpose, but will only work well for two or 
three hours. 

Had no other method of producing current electricity 
been discovered, the art of electric lighting would still 
have been only an electrical curiosity ; but the nume¬ 
rous forms of dynamo-electric machines recently in- 
vented have made the production of the electric light 
comparatively cheap, and have given the art a great 
impetus. It will be readily seen, however, that to ap¬ 
ply the name voltaic arc to an electric arc jiroduced by 
electricity evolved by a machine is a palpable incon¬ 
gruity. In Davy’s experiments, about the beginning of 
the present century, he produced a light with an arc 
four inches long, in the open air, by using a battery of 
some two thousand cells. 

236 . What is an electric-arc lamp f 

An electric-arc lamp, frequently called a regulator , is 
a device or apparatus constructed for the purpose of 
maintaining the electrodes of the arc at their proper dis¬ 
tance from fine another. Such a contrivance becomes 
necessarv, because the carbons are continually burning: 
away, and if some means were not adopted for carry¬ 
ing them forward, and keeping them at the proper dis¬ 
tance apart, the light would soon be extinguished. 

Much ingenuity has been displayed in the construc¬ 
tion of these lamps and regulators, and many extraor¬ 
dinary arrangements have been devised, only a few of 
which have survived and gone into extensive use. 

“ In some of these the carbons are attached to guides 
actuated by trains of wheels, which push them forward 
at the necessary speed. The wheels are put in action or 


MISCELLANEOUS APPLICATIONS OF ELECTRICITY. 269 

stopped, as tlie case may be, by means of electro-mag¬ 
nets forming part of the electric circuit of the lamp. 
Most of these electric lamps are arranged so that when 
the lamp, from any cause, goes out, the carbons are 
brought into contact for an instant, and as soon as the 



Fig. 95. 


current is thus re-established the carbons are drawn 
back to the required distance.” * 

The movement which is most frequently used in 
America is one wherein the attraction of a solenoid, 
acting upon a movable iron core, regulates the dis¬ 
tance between the carbons. Such a lamp is that of C. 
F. Brush, which is shown in Figure 95, and which, be- 

* “ Electric Light,” by A. Bromley Holmes. 






























































270 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

sides being capable of regulating tlie distance between 
tlie carbons, automatically short-circuits, or cuts itself 
out, when defective, thus permitting the current to flow, 
as it were, round the lamp in the main circuit. 

As this lamp is quite extensively used, its operation 
will be fully described. 

The circuits are shown in the diagram, Figure 96 ; the 
lower carbon, K', is fixed, and the upper one, K, is at¬ 
tached to a metallic rod which, by means of a washer 
clutch, W, is connected with an armature carried by a 



pair of plungers, arranged to slide in and out of a pair 
of solenoids, or helices of covered wire, H H. These 
solenoids are wound in multiple arc with two wires, 
which are wound oppositely with respect to one another. 
The first of these wires is in direct circuit with tlie arc, 
and consists of a few layers of coarse wire, through 
which the main portion of the current operating the 
lamp passes to the rod of the upper carbon. The up¬ 
per carbon falls by the action of gravity against the lower 
carbon, and when the two carbons are together the cur¬ 
rent passes on from the upper to the lower, and thence 
out. 



































MISCELLANEOUS APPLICATIONS OF ELECTRICITY. 271 

Entering the lamp at the binding post X, the path of 
the circuits, which are three in number, are as follows : 
The circuit through the lamp carbons is from the point 
1, b\ the parallel wires 2, constituting the coarse-wire 
helix round the solenoids, H, and by the wire 5 to 
the carbon-holder, X, and thus through the arc to the 
terminal, T, and on to the next lamp. The second cir¬ 
cuit is composed of much finer wire, and, branching from 
the main line at the point 1, passes by the parallel wires 
3 through the solenoids, being in practice wound over 
the layers of coarse wire; issuing from thence by the 
wires 4, it is led round the electro-magnet, E, and out to 
the binding-post Y by the wire 6. 

Thus the fine wire forms a secondary circuit of high 
resistance through the lamp, which circuit is indepen¬ 
dent of the arc between the carbons, and is always closed. 
It follows from the difference in direction of the current 
in the two helices, that the fine-wire helix will con¬ 
stantly tend to neutralize the magnetism produced by 
the coarse-wire or principal helix. The number of con¬ 
volutions of the fine-wire helix and its resistance are so 
proportioned to the number of convolutions in the prin¬ 
cipal helix, and its resistance together with that of the 
normal voltaic arc, that the magnetizing power of the 
latter shall be much greater than that of the former. 
Notwithstanding the small amount of current which 
passes through the fine-wire helix (about one per cent, 
of the whole current), its magnetic power is very consid¬ 
erable owing to its great number of convolutions. 

Now, when the arc of any lamp becomes too long the 
resistance of its main circuit is thereby increased and 
more current is sent through the secondary or fine-wire 
coil; the magnetizing power of the solenoid, of course, 
being thereby weakened, allowing the carbons to ap¬ 
proach. On the other hand, if the arc becomes too short 
its resistance is reduced, less current goes through the 
fine-wire helix, and the magnetic strength of the sole¬ 
noids are correspondingly increased. The plungers are 


272 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


sucked into them, carrying the armature, H, and lifting 
one end of the ring-clutch, W, and the upper carbon- 
holder with it, and thus the arc is maintained. In prac¬ 
tice the resistance of the fine-wire helix or helices in 
each lamp is rather more than 450 ohms, while the re¬ 
sistance of the coarse wire, various connections, carbons, 
and voltaic arc, in each lamp used with the sixteen-light 
machine, is about 4.5 ohms. Hence not more than 1 
per cent, of the whole current is diverted from the arc. 
The resistance of the coarse-wire helix, carbons (copper- 
coated), connections, etc., in each lamp is very small. 
To determine this resistance 16 lamps were connected in 
series in the usual manner, about 200 feet of No. 10 cop¬ 
per circuit wire being used. Full length carbons were 
then placed in the lamps, and the upper and lower car¬ 
bon of each lamp were connected by means of a strip of 
sheet copper wired to each carbon. The resistance of 
the whole set was then measured and found to be 2.10 
ohms, showing a resistance for each lamp with its car¬ 
bons of 0.131 ohm. This is 2.91 per cent, of the whole 
resistance of the lamp when in operation. To this loss 
must be added the 1 per cent, due to that amount of 
current diverted from the arc by the line-wire regulating 
helix, making a total loss of 3.91 per cent. The remain¬ 
ing 96.09 per cent, of the whole energy absorbed in each 
lamp appears in the arc between its carbons. The third 
branch circuit through the lamp is only completed when 
the resistance in the arc becomes abnormally great, or 
when the arc from any reason fails. 

It constitutes the short-circuiting or cut-out device, 
and is operated by the electro-magnet, E. The core of 
this magnet is surrounded by two coils just like the 
solenoids, but, unlike them, its coils are both wound in 
the same direction. The fine-wire coil, as already de- 
scribed, is a continuation of the fine-wire solenoid helix. 
The thick-wire coil, which is only brought into action 
when the lamp is to be cut out, starts from the stud, M', 
passes round the core, and then unites with the terminal 


MISCELLANEOUS APPLICATIONS OF ELECTRICITY. 273 

wire 6 of tlie fine coil, passing out to Y. The armature, 
B, of the electro-magnet, E, connects by a suitable wire, 
7 R, with the screw-post, X. 

The armature-lever of the electro-magnet is suitably 
pivoted, and is united by the wire R, which may be 
made of any required resistance, to the incoming line- 
wire before it reaches the solenoids. If now the arc fails 
or if its resistance is excessively increased, a large pro¬ 
portion of the current goes through the fine wire of the 
electro-magnet, which thus becomes more strongly mag¬ 
netic, and strong enough to attract its armature. The 
armature, being attracted, closes the circuit of the thick 
wire. If the trouble in the arc is permanent the short 
circuit is now maintained through the thick wire cutting 
the arc completely out. If, on the contrary, it was 
merely caused by the undue length of the arc, as soon 
as the short circuit is made through the thick wire of 
the electro-magnet the solenoids lose their power, the 
upper carbon falls on the lower one, the electro-magnet 
in its turn is short-circuited, the solenoids resume their 
power, and the light is reinstated by reason of the car¬ 
bons taking their proper distance apart. The entire 
series of operations, though taking a long time to de¬ 
scribe, are the work of an instant, so that the light, 
though subject to continuous regulation, is practically 
maintained without any cessation, except when com¬ 
pletely disabled ; when it is immediately short-circuited. 

The lamp thus described, and all of the types treated 
of in the above explanation, are of course adapted only 
for the production of the arc light, and where other va¬ 
rieties of electric light are required other forms of lamp 
become necessary. 

237. What is meant by the incandescent electric light l 

The incandescent light is that produced by the pas¬ 
sage of a strong current of electricity through an im¬ 
perfect conductor or a conductor of high resistance. 

It is based upon the principle that when such a cur¬ 
rent is passed through such a conductor the substance 


274 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

of the conductor becomes heated ; and if it be attenu¬ 
ated—as, for example, in the case of a piece of fine wire 
or a thin carbon pencil or filament—after a certain de¬ 
gree of heat is reached, say above two thousand degrees 
Fahrenheit, it glows with light, the brilliancy of the 
light depending upon the strength of the current. 

Lighting by incandescence has ever been a favorite 
idea of inventors and experimentalists in electric lighting, 
but only within the last few years can it be said to have 
achieved any important success. Contrary to the gene¬ 
ral opinion, this idea is by no means new, since as early 
as 1845 an American inventor named Starr patented in 
England a lamp which is shown in Figure 
97, and which was intended to operate on 
this principle. 

This lamp consisted of a conducting wire, 
I), sealed into one end of a glass Torricellian 
vacuum-tube, and connecting with a carbon 
rod, A, whose lower extremity is in contact 
with a second conductor, C, which rests in the 
quicksilver. A non-conducting bar, B, car¬ 
ries brackets in which the carbons are sup¬ 
ported. The subject, after temporary re¬ 
vivals in 1850 and 1852, dropped out of 
sight, chiefly on account of the lack of an 
economical generator of electricity ; but in 
1873 was again taken up by Lodyguine, a 
Russian inventor. 

Since then it has assumed a steadily in¬ 
creasing importance, Edison, Weston, Max¬ 
im, Sawyer, and Bernstein working upon it 
in America, and Swan and Lane-Fox in 
England. 

Considerable success has attended their 
efforts, and one of the most, perhaps the 
most important installation, is that of Mr. 
Edison, who, after many months of patient and con¬ 
tinuous labor, has succeeded in illuminating a number 

























































MISCELLANEOUS APPLICATIONS OF ELECTRICITY. 275 


of business places and houses throughout an extensive 
district in New York City from a single central lighting 
station. 

After many experiments with iridium and platinum, or 
alloys combining or containing these metals, all the in¬ 
ventors ultimately have decided that carbon is the only 
suitable known substance to maintain in the incandescent 
state as an illuminator. Experience has also demon¬ 
strated that some method of protecting the light-giving 
part from the oxygen of the atmo¬ 
sphere is necessary, the carbon other¬ 
wise being rapidly consumed. For 
this reason Edison, Swan, Lane-Fox, 

Weston, Maxim, and Bernstein use 
lamps in which the deleterious action 
of the oxygen is prevented by enclosing 
the incandescing conductor in vacuo ; 
while Sawyer encloses his carbons in 
globes tilled with nitrogen. 

238 . What are the distinctive features of 
the different incandescent electric lamps t 

The Edison lamp, as now made, has 
for a light-producing part a carbonized 
filament of bamboo. This is enclosed 
in an exhausted glass globe, and by 
means of fine platinum wires is con¬ 
nected to a screw and sole-plate,which, 
when screwed on to a bracket or stand, 
make contact with the two external 
conducting wires. In the construction 
of these carbon filaments Mr. Edison made many ex¬ 
periments to ascertain the best material to be employed, 
and, after carbonizing a large number of vegetable fibres 
and tissues, arrived at the conclusion that certain kinds 
of bamboo presented the greatest advantages, both for 
facility of manipulation and for uniformity of structure. 
The shape of the carbon filament used in this lamp 
is that of an inverted U, as shown in Figure 98. 






















276 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


The Swan lamp-carbon is formed of cotton thread 
converted by treatment with sulphuric acid into a 
parchment-like material, and carbonized. The finished 
carbon is looped with a double turn at the top, as in 
Figure 99. The ends of the strip are thicker than the 
middle, and are joined to the conducting wires by 
metal clamps. 

The Lane-Fox lamp is represented by Figure 100, 




and in it the carbon filament is made from the fibres 
of Italian grass, or bass-broom. A peculiar method of 
carbonizing is involved in its preparation. 

Figure 101 shows the Maxim lamp, which is distin¬ 
guished by an incandescing carbon made from card¬ 
board and shaped like the letter M. 

The light giving conductor in the Bernstein lamp con¬ 
sists of a hollow cylinder of carbon supported at each 
end in a carbon socket. 




















MISCELLANEOUS APPLICATIONS OF ELECTRICITY. 277 


The Weston lamp is similar in appearance to the 
Maxim, but the tilament is made of lion-fibrous cellu¬ 
lose, which is afterward carbonized. This material is 
extremely tough and elastic, and 
has a high resistance. 

239. How is the illuminating poiver 
of a light generally expressed 9 

The standard unit of measure¬ 
ment of light in this country and 
England is a sperm candle burn¬ 
ing approximately one hundred 
and twenty grains of spermaceti 
per hour. In France the carcel 
lamp is the unit; this lamp 
burns forty-two grammes, or six 
hundred and forty-eight grains, 
per hour. In Germany the unit 
is a paraffine candle of which six 
weigh five hundred grammes ; one 
carcel is equal to about seven and 
one-half of these candles. All of 
these standards are crude ap¬ 
proximations, and it has been 
suggested among other plans that 
the unit should be derived from the area of floor which 
any light is capable of illuminating. 



Fig. 101. 


240. ^Vhat is meant by the term electric candle i 
The electric candle is really nothing more than a pecu¬ 
liar arc lamp reduced to its simplest form. It consists 
of a pair of small carbon-rods placed parallel to each 
other, with a thin strip of plaster-of-Paris or fine clay 
between them as an insulator. This being in the shape 
of a candle, together with the fact that the light com¬ 
mences at the free ends and burns downward as the 
carbons consume away from one end, like the wick and 
combustible material of a candle, account for the name. 
The candle is the invention of a Russian engineer, M. 
Jablochkoff, and was patented by him in March, 1876. 





































278 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

Its use dispensed with the cumbrous and complicated 
lamps and regulators then in use, and gave an impetus ta 
electric lighting which is still felt. The sticks of car¬ 
bon which constitute the candle are only about one- 
sixth of an inch in diameter and from nine to ten inches 
in length, although they have been made as short as six 
and a half inches. The shorter ones only burn one 
hour. When the current of electricity passes, an arc 
of light is maintained across the top of the carbons, 
which are gradually consumed as an ordinary candle 
is, together with the insulating material. The circuit 
before the current passes is completed, and the candle 
lighted by laying a small piece of graphite or black lead 
across the top of the carbon sticks. The currents em- 
ployed are of an alternating character, so as to consume 
both of the carbon sticks equally fast. These candles 
are more used in France than elsewhere, although they 
have been employed to a considerable extent in London. 
Four candles are usually placed in an opalescent glass 
globe, and an automatic arrangement provided to switch 
the current from one candle to the next as each burns 
down. 

The electric candle has been much improved by the 
well-known electrician and inventor, Mr. Henry Wilde, 
of Manchester. He remarked the small part apparent¬ 
ly taken by the insulating material, and diminished that 
material by discontinuing the plaster-of-Paris and mere¬ 
ly coating the carbons with a hydrate of lime. No dif¬ 
ference in the operation of the candle being observed, he 
went a step farther and arranged the carbons without 
any insulator or separating medium at all, finding the 
light to be absolutely improved thereby. He further 
observed that even when the circuit was completed at the 
bottom or lower end of a pair of carbons, the arc or 
light would immediately ascend to the points. He next 
arranged an automatic lighting device by making one of 
the carbon-holders with a hinge at the bottom, and con¬ 
tinuing it horizontally in the form of a right-angled lever,. 


MISCELLANEOUS APPLICATIONS OE ELECTRICITY. 279 

the horizontal part serving as the armature of an electro¬ 
magnet, the helices of which are included in the light¬ 
ing circuit. By its weight the carbon, and its holder, 
which is hinged, lean against the fixed carbon as long 
as no current is flowing; but as soon as a current com¬ 
mences to flow, the circuit being completed at the point 
where the carbons touch one another, the electro-mag¬ 
net is charged, attracts the armature, and draws the 
hinged carbon-holder to an upright position, and so 
brings the carbons to the requisite distance from one 
another. 

241. What are semi-incandescent electric lights t 

These, which are also sometimes called incandescence- 
arc lamps, are constructed either by arranging a carbon 
rod to press against a block of carbon, or by having two 
carbon electrodes, with a piece of refractory non-conduct- 
ing material, such as marble, interposed between them. 

In the first case the light is produced by the passage 
of the current through a rod of carbon, which, at the 
end that presses against the block, is so small that its 
extremity becomes heated nearly to whiteness. 

Also, when the pressure is very slight, small arcs are 
developed at the point of contact, which aid in produc¬ 
ing the light. 

Of this category are the lamps of Regnier, Werder- 
mann, and Varley. 

In Werdermann’s lamp a rod of carbon is forced up¬ 
wards by the action of a weight against a rounded block 
of carbon ; the rod becomes incandescent at its extre¬ 
mity, gives a strong light, and is gradually consumed. 
Varley’s lamp is one of the earliest of this class, and 
consists of a disc of carbon with bevelled edge, on 
which rests the extremity of a carbon pencil mounted 
at the lower end of a pivoted lever. Regnier’s lamp is 
an improvement on the foregoing, and comprises a rod 
and a disc of carbon ; the rod as it falls imparts motion 
to the disc, which is thus caused to revolve, and con¬ 
tinually presents fresh points of contact. 


280 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

In the second case the light results from the passage 
of the electricity over the surface of the block of marble, 
or other analogous substance, which is between the car¬ 
bon electrodes. This, by the intense heat, is made in¬ 
candescent, and its incandescence adds to the light of 
the arc between the electrodes. The most familiar lamp 
of this class is called the Sun Lamp (Lampe Soleil). This 
light is very steady, is of a golden hue, and has an 
advantage in the stored-up heat in the incandescent 
block, which, if the current weakens momentarily—for 
example, by reason of a slackened driving belt—is suffi¬ 
cient to supply the deficiency for a short time. It is 
said, however, to be very wasteful of power. 

The earliest worker in both of these classes was W. 
E. Staite, of London, who, between the years 1846 and 
1849, took out several patents in England for different 
plans of electrical illumination. 


CHAPTER XIX. 





ELECTRO-METALLURGY. 

242. What is electro-metallurgy f 

It is the art which governs the electro-deposition of 
metals upon any surface prepared to receive them, from 
a metallic solution. It is based upon the observed fact 
that a current of electricity passed through such a solu¬ 
tion tends to decompose it into its constituents—water 
and the metal held in solution ; depositing the latter, as 
before stated, upon any prepared surface. The two great 
divisions of electro-metallurgy are electro-plating and 
electro-typing. 

243. What is electro-plating f 

It is that division of the art of electro-metallic deposi¬ 
tion which treats of depositing a permanent coating of 
metal by means of electricity. Although we are accus¬ 
tomed to speak of electro-plating only when referring 
to the deposition of silver and gold, we may with per¬ 
fect correctness apply the term to any other metal also. 

To electro-plate is to provide a chemically clean me¬ 
tallic surface, to immerse that surface in a metallic solu¬ 
tion, and by means of electricity to cause the metal 
contained in the solution to be deposited upon the im¬ 
mersed surface in such a manner that it may perma¬ 
nently incorporate itself with the original surface ; and 
so, whatever may be the material of which the original 
surface is composed, after plating it will appear like 
whatever metal is deposited on it, whether that metal 
be silver, gold, copper, nickel, or anything else. As 
already indicated, the article to be plated must be 
chemically clean. The source of electricity employed 

may be either a voltaic battery or a dynamo-electric 

281 


282 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

machine. If the plating establishment is a commercial 
one or doing business on a large scale, a machine is de¬ 
cidedly to be preferred. For experimental work a bat¬ 
tery is the most convenient. For most work of the 
ordinary character, either in copper, silver, or nickel, 
the large Smee battery is most universally useful. The 
Daniel 1 battery may be used for small current work, 
such as gilding; and the carbon battery can be profit¬ 
ably employed where a strong current is required, as in 
depositing brass or iron. 

The process is represented in Figure 102, where O is 



Fig. 102. 


the depositing battery, C the vessel containing the solu¬ 
tion, D a metallic rod connected with the positive pole, 
having a plate of metal suspended from it and dipping 
into the liquid ; B is another rod, connected with the 
negative pole of the battery, and from which the articles 
to be plated are suspended. These articles are thus 
made the negative pole of the battery, and the metal 
plate suspended from D becomes the positive pole. 

The dynamo-electric machine has within the last ten 
years to a great extent superseded the batteries in fac¬ 
tories, and the forms of machine favored are chiefly 
those of Gramme and Weston, but any dynamo machine 
of small internal resistance, furnishing constant currents 
of non-alternating direction, may be successfully used. 

Electro plating is one of the most useful of arts, and 




































































ELECTRO-METALLURGY. 


283 


series either to protect a valuable surface, or to beautify 
a surface, or ornament and give an appearance of value 
to articles of ordinary character. 

244 . What is electro-typing t 

By electro-typing is meant the production of copies in 
metal of any object by means of the action of electricity. 
It differs from electro-plating in that the metal deposited 
on the article subjected to the process is not intended 
to remain permanently, but merely, as it were, to form 
itself upon, and assume the shape of, that article. While 
the electrical features are the same as in electro-plating, 
and while the art is dependent upon exactly the same 
principle, the technical details are completely dissimilar, 
since in the former art all the skill of the operator is 
directed to the establishment of a permanent adherent 
coating of metal, while in electro-typing his efforts are 
oppositely directed, and all the details of the process 
must be arranged to admit of a ready separation of the 
deposited metal from the original article. 

245 . Give a brief outline of the art of electro-typing. 

This art was first introduced as early as 1838 by Pro¬ 
fessor Jacobi, of St. Petersburg, in a paper communi¬ 
cated by him to the Academy of Sciences of that city, 
in which he explained a process of producing copies of 
engraved plates by means of electricity. 

Almost at the same time Mr. Thomas Spencer, of Liver¬ 
pool, made public a series of experiments in which he 
had been engaged on the same subject; while nearly sim¬ 
ultaneously a printer named Jordan described similar 
experiments which he had made about the same time. 
In this, as in other great discoveries, it thus appears that 
several experimentalists were close to each other on the 
same track at once ; but Spencer was by far the most 
painstaking of the three, and demonstrated its practical 
value. 

The entire process is founded upon a very simple prin¬ 
ciple—namely, that certain metals can be deposited from 
a solution of their salts by the passage through that so- 


284 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

lution of a current of electricity. The primitive methods 
adopted in the early days of the art are now obsolete, 
except as used by amateurs ; nevertheless, as they em¬ 
body the above principle as well as the most recent 
inodes can do, and also possess the cardinal virtue of 
simplicity, they are here noticed. 

A modification of the Daniell battery, such as is 
shown in Figure 103, was generally used, 
consisting of a glazed earthenware or glass 
cell containing a solution of sulphate of 
copper, kept at the proper strength by ex¬ 
tra crystals on a shelf. A porous cup con¬ 
taining dilute sulphuric acid stood in the 
jar, holding an amalgamated zinc rod. 
The object to be copied, or electro-typed, 
whether a coin, medal, a seal, or other 
article, was attached by a copper wire to 
the zinc of the battery and suspended in the 
solution. This object thus formed the ne¬ 
gative plate of the voltaic cell, and an electrical current 
passed from the zinc, through the two liquids and the 
porous cup, to the object to be copied, and back to the 
zinc rod through the wire, completing the circuit. 
When the circuit was closed the zinc dissolved and 
formed its sulphate; the copper solution was also de¬ 
composed and its copper deposited on the object to be 
copied. Any part not required to be copied was coated 
with varnish or some other non-conductor. The deposit 
was separated from the object when sufficiently thick, 
and found to be an exact fac-simile of the original 
article. 

Such is the art of electro-typing in its crudest me¬ 
thods, but substantially identical in every essential fea¬ 
ture to the same art as practised with every modern 
appliance. If the model be not a conductor it becomes 
necessary to coat the surface to be copied with some me¬ 
tallic powder (black-lead is generally used), applied over 
the surface with a fine brush. It is evident that by this 











ELECTRO-METALLURGY. 


285 


device we are enabled to use as models plaster-of-Paris, 
wax, gutta-percha, or any fusible or plastic substance. 
It was early discovered that the use of a separate bat¬ 
tery, as shown in Figure 104, was a great improvement; 
when this was used a bath of the solution of the metal 
to be deposited was prepared, and the copper plate of 
the battery connected with a second copperplate sus¬ 
pended in the solution, while the articles to be copied 
were also suspended in the solution and united by a wire 



to the zinc plate of the battery. When so disposed the 
suspended copper plate dissolves, adding copper to the 
solution as fast as it is abstracted from it by deposition 
on the articles to be copied. As in the sister process of 
electro-plating, the use as a generator of the dynamo- 
electric machine lias greatly advanced of late years, 
and it is now employed in all large establishments. 

The electro- typing process finds many uses : it is uni¬ 
versally employed to produce copper duplicates of wood 
engravings, and set-up type is often thus copied ; sta¬ 
tuettes, medals, and coins can be thus reproduced 
without limit, and many electro-type copies are fully as 
beautiful as the originals. 


t 

















































CHAPTER XX. 


ELECTRIC BELLS. 


246. How is electricity made to ring bells % 

Practically in the same way in which it is made to 
operate a telegraph. An electro-magnet is fitted with 

an armature; that arma¬ 
ture is pivoted, and its 
lever extended to the 
necessary length and 
furnished at its free 
end with a bell-liam- 
mer, which, when the 
electro-magnet is excit- 
ed and the armature 
consequently attracted, 
strikes upon a gong 
with more or less force. ' 
This is shown by the engraving, Figure 105. 

There are several ways in which electricity may be 
utilized for this purpose. The method already described 
may be varied by so disposing the several parts that 
the armature and hammer are attracted away from the 
gong when the electro-magnet is charged by the closing 
of the circuit, while when the circuit is again broken 
the hammer, being retracted by a spring, strikes the 
gong. Sometimes the bell is so constructed as to ring 
when the direction of the current is reversed, and the 
bell is then called a polarized bell. At other times, 
when a heavy stroke is required, while the power 
exerted by the current is but feeble, the hammer is 
impelled by a weight or spring acting through a train 

of clock-work, the electricity in such cases merely act- 

286 




















ELECTRIC BELLS. 


287 


ing as a controller to release and detain the clock¬ 
work. 

247 . What is a single-stroke electric bell % 

It is a bell comprising an electro-magnet, an armature 
operated by the same, and a hammer extending from 
the armature, which may be arranged to strike its gong 
a single stroke or tap at the moment either of breaking 
or making the circuit; of changing the direction of the 
current; or both ; at the will of the manipulator. The 
name single-stroke is colloquially applied to such a 

bell in contradistinction to a bell giving a continuous 

ring. 

248 . What is a vibrating or trembling electric bell f 

It is an electric bell which, in addition to the ele¬ 
ments possessed by the single-stroke bell, lias some 
device adapted to alternately allow the electricity to 
pass through the electro magnet helices and shut it 
off from them, so that as soon as the hammer is so far 
drawn up as to strike the bell it is drawn back again 
once more to be attracted, and again withdrawn, and so 
on as long as the circuit is kept closed at the point 
of manipulation ; that is, if a bell of this character be 
placed in the circuit of a battery, the said circuit also 
passing through a key which is normally open, when 
the circuit is closed by pressing the key, the magnet 
will become charged and will attract the armature, and 
the bell-hammer attached to the armature will com¬ 
mence to alternately strike the bell and withdraw from 
it, and continue so to do until the key is once more 
opened. 

This kind of bell usually is arranged by leading the 
circuit of the bell-magnet through the armature-lever 
itself, and from it to the back limit-stop, thence to 
the binding-post; thus when the armature is attracted 
under the influence of the current, it has only time to 
strike the gong before the circuit is broken by the 
withdrawal of the lever from the back limit, and it is 
compelled to recede. The lever is usually furnished 


288 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 



Fig. 10G. 


with a platinized spring, which improves the contact, 
and at the same time gives the armature an im¬ 
pulse and prevents it from breaking the 
circuit prematurely. Figure 106 repre¬ 
sents one of the most frequent forms of 
the vibrating bell. There are several 
other ways of constructing vibrating 
bells, but the foregoing is for ordinary 
use the best way. 

249. Hoiv is a polarized bell constructed f 
Quite a variety of polarized bells are 
made, and used for special purposes. 
Two, however, are sufficient to exemp¬ 
lify the principle. The first, and until 
the days of the telephone the most 
usual form, has substantially the same 
construction as a Siemens polarized relay (Q. 192). 

A base of hard steel is made in the shape of a right 
angle ; on the horizontal or flat side of the steel base an 
electro-magnet is transversely placed, so that if the end 
of the flat side is of north polarity the same polarity is 
by induction continued through the electro-magnet, and 
both of its poles become north poles. The other end of 
the angular steel magnet is, of course, a south pole, and 
is forked ; one end of a slender rod of iron is pivoted in 
this fork, and the other extends outwardly until its end 
rests between the two extremities of the electro-magnet, 
which are fitted with adjustable pole-pieces. 

As shown in Figure 107, which represents a modifi¬ 
cation of this type of polarized bell, an extension-rod 
provided with a hammer is attached to the end of the 
iron rod which serves as an armature, and in its range a 
bell is placed. When the electric impulses sent from a 
magneto-generator, or a battery and pole-changer, are 
passed through the coils of the bell-magnet, the arma¬ 
ture vibrates from side to side and rings the bell. 

Such a bell, though strong and reliable where com¬ 
paratively slow alternations of current are sent, is rather 
















ELECTRIC BELLS. 


289 


sluggish in its action when the alternations of direc¬ 
tion are very rapid. This fact led to the introduction 


Fig. 107. 



of the second form of polarized bell, which is now to be 
described. This is the form so familiar to us in the 
regulation telephone bell-box. In this bell, as in the one 
already described, an electro-magnet is fixed upon one 
end of a permanent magnet, while near, but not neces¬ 
sarily attached to the other end of the permanent mag¬ 
net, a soft-iron armature is pivoted by its centre, and 
carries by a light metal rod the bell-liammer. The per¬ 
manent magnet is Fig.ios 

in shape like a 
bar magnet, with 
each end bent for 
about an inch at 
right angles to 
itself; one of 
these bent ends is 
placed behind the 
heel piece of the 
electro-magnet, 
and the other be¬ 
hind the centre 
of the pivoted 
armature. Two gongs are arranged in front, between 



a 



- 1 _ i 
























































290 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


which the bell-hammer vibrates, striking each alter¬ 
nately. When an electric pulsation of positive direc¬ 
tion is sent through the coils of the electro-magnet 
the armature swings over to one side, and when a 
pulsation of negative direction is sent it swings over 
again to the other side. Figure 108 represents the 
working parts of a bell of this character. 

Rapidly alternating electrical currents, generated 
either by a magneto-machine or by a battery having 
a pole-changer in circuit, are used to operate these bells, 
and in practice a generating magnet and coil is attached 
to each one, and placed in the same case, immediately 
below the bell, so that each instrument possesses not 
only the power of ringing but also that of operating 
other bells. 

250. Hoic must the apparatus and wires be arranged for a 
simple bell circuit , where one bell is to be rung from but one 
point , and what apparatus is required t 

All that is required is one bell, one press-button, or 
key, as much battery as may be found necessary (for any 
distance short of fifty feet one cell of Leclanche will do), 
and enough wire for about twice the distance between 
the button and the bell. To set up the apparatus, screw 
up the bell to a support where it is wanted, then mea¬ 
sure off the wire, taking care to have the pieces long 
enough. Find a place for the battery and set that up ; 
then attach to the terminal screws of the press-button 
two wires, one extending to the bell, and the other to 
the battery ; having attached them to the press-button, 
screw up the button in its place and put on its cover. 

In Figure 109 the connections are clearly shown, II 
indicating the bell-hammer, E the electro-magnet, C the 
automatic circuit-breaking points, P the press-button, 
and B the battery. Figure 110 shows a vertical section 
of the press-button, which clearly explains its operation. 
One of the press-button wires is connected with one of 
the bell binding-screws, and the other to one pole of the 
battery. A third wire must now be made to unite the 


ELECTRIC BELLS. 


291 


remaining bell terminal to the other battery pole ; this 
done, the construction is complete. The circuit may 
now, referring to the figure, be readily traced: com¬ 
mencing at the positive pole of the battery, and fol¬ 
lowing the arrows, the circuit is first to the press-button, 
where it is ordinarily open, then to one of the bell ter¬ 
minals, through the bell-magnet to the armature-lever, 
through the lever to the points C, then to the outgoing 
terminal, and thence back to the negative pole of the 
battery. 

For good work the wires must be well insulated by 
being covered with cotton, or, if they are to rest in damp 
places, with kerite or india-rubber ; of course, before 






Fig. 110. 


making connections, the ends of the wire must be care¬ 
fully stripped for about an inch and a half. The wires 
should be neatty tacked to the walls, or otherwise 
.secured. More than one wire must never be placed 
under one staple, and the entire work must be made 
as neat as possible. It is just as easy to make a hand¬ 
some job as an unsightly one. This is the simplest plan 
for a signal-bell circuit, and may readily be constructed 
by any one. 


























292 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


251. How may electric bells be operated by a pull, similar 
to the ordinary mechanical door-bell f 

By using a pull circuit-closer, like that shown in 
Figure 111, instead of a press-button. 

As shown, the circuit-closer consists in a pair of 
springs, B 13, mounted on a block of non-conducting 
material, like hard rubber, and connected respectively 
with the bell and battery wires, but not touching one 
another when in a state of rest. A hole is bored 
through the insulating block, and a rod ending at the 
inside in a metal disc, C, and surrounded by a helical 

spring, is passed through, and 
fitted at its outside end with the 
flange and knob, P. The helical 
spring serves to keep the disc, C, 
away from the ends of the flat 
contact-springs, B, and also to 
draw in the knob after it is pulled 
out to close the circuit. When 
the knob is pulled the helical siting is compressed, and 
the disc, C, makes contact with both of the flat springs, 
B, thus closing the circuit. The pull circuit-closer is 
well adapted for use in connection with door-bells. 



Fig. 111. 


252. How may we arrange a circuit to ring a single bell 
from two or more separate points t 

Such an arrangement may be easily understood by 
reference to the engraving, Figure 112. Setting up the 
bell and battery as before, connect one pole of the 
battery with one of the bell binding-screws by a wire; 
then run a wire from the other battery pole past and 
near to all the press-buttons, at the points from which it 
is desired to ring, terminating at the most distant press- 
button, to which the end of the wire, after being bared, 
is attached. At each of the intermediate buttons branch 
wires are extended from this battery wire in the follow¬ 
ing manner: At the nearest point of the battery wire 
to each of the buttons strip its covering from it for a 
space of about an inch, and scrape the wire thus bared 








ELECTRIC BELLS. 


293 


m 


I 

I 

i 

h 

t, 




777777 






llllll 




Gk 


2222222^222 


PARLOR 




i^ill it is bright; the wire at these points then presents 

the appearance in¬ 
dicated at A, Figure 
114. Then bare 
about three inches 
of the ends of the 
proper number of 
branch wires, and 
wind the bared ends 
round the stripped 
portions of the bat¬ 
tery wire, as at B, 
Figure 114; this, 
especially if solder¬ 
ed, makes a good 
splice. The free 
ends of the branch 
wires, after being 
bared, are attached 
each to one screw 

of their respective 

press-buttons, which 
may be at any dis¬ 
tance from the 

immmmm main battery 
wire. In some 
cases two of 

the buttons may be very near together ; the branch 
may then be connected to the main line in the manner 
represented in d 

Figure 113; c c /} 

being the main \ \ 

wire, d the 

branch to one 

of the buttons, 
and e the branch to the other. At this point in con¬ 
struction we have a battery wire extending by branches 
to each press-button. Finally, as in the figure, a simi- 



ii 

ft 


KITCHEN 


7777777777 


Fig. 112. 



y e 


Fig. 113. 































294 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

lar main wire is run from the remaining bell terminal 

to the most distant button, 
- [— r - branching to the intermedi¬ 
ate ones, precisely the same 
way as is done in the bat¬ 
tery wire. It is obvious 
now that a bell circuit nor¬ 
mally open is constructed, 
which is capable of being closed at any of the buttons. 

253. How must the wires he arranged to ring two hells 
from a single button or circuit-closer f 

The apparatus required is a battery, a press or pull 
button, or key, and the two bells which are to be rung. 
These may, if required, be in different rooms. 

The arrangement is indicated in diagram by Figure 
115. One of the battery wires runs directly to one of the 




tended to one binding-screw of each of the bells, as 
shown. A third wire is led from the other push-button 
screw, and branches to the remaining binding-screw of 
each bell. When the button is pressed the current 
divides between the two bells, and thus they are both 
rung. Another way to do this is to provide but one vi¬ 
brating bell, allowing the other bell to be a single-stroke 
bell; they must, when this plan is adopted, be arranged 
in series, or directly after one another in circuit, and the 
second, although in itself a single-stroke bell, will vi¬ 
brate in unison or harmony with the intermissions of 
the current produced by the vibrator. In either of the 































ELECTRIC BELLS. 


295 


above ways several bells may be operated, from one 
button or circuit-closer with one battery. 

254 . Describe a plan whereby an answering press-button 
may be combined with each of a series of bells , so that a re¬ 
sponsive ring may be sent. 

Such a device is shown by the diagram in Figure 116. 
The same battery is made to serve for the ringing in 
both directions. One pole of the battery, B, has a wire 
leading past all the bells, b , to the most distant one, 
branching to one terminal of each bell in passing. Call 
this wire No. 1. 

From the other pole of the battery a wire is led which 
branches in two direc¬ 
tions. One branch leads 
to a press-button, P, the 
other to the response 
bell, R. From the other 
screw of the press-button 
a wire, 2, is led to the 
most distant bell, branch¬ 
ing to each bell en route 
in the same manner as 
No. 1. Now run a third 
wire, No. 3, from the 
remaining terminal of 
the response bell, R, to a 
point near to the most 
distant bell, b , there con¬ 
necting it to one screw 
of the answering button, 



P, the other screw of the 
same button being con¬ 
nected by a short wire 
to main wire, No. 1. In 



Fig. 116. 


„ — - - 7 

like manner from No. 1, near each of the bells, b , short 



























296 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

wires are run to the answering buttons, P, which by their 
other screws are connected with the response wire, No. 3. 
By this arrangement a pressure of the button, P, will 
simultaneously ring all of the bells, b; and when any 
of the buttons, P, are pressed, the bell, P, will be rung. 

255 . Describe the circuit connections of a bell line of two 

stations , each of the said sta- 
|| tions being capable of signal- 
|| ling the other. 

This arrangement will be 
understood by reference to 
Figure 117. The line at 
each terminal station con¬ 
nects with the key, K, 
which by its own resili¬ 
ency presses against its 
back stop or contact, b , 
this in turn being connect¬ 
ed by insulated wire with 
one of the bell terminals, 
the other being attached 
to a ground or return 
wire. When the line is at 
rest its condition is as 
shown in the engraving ; 
the key at both stations 
being elevated, and the 
bells being both maintain¬ 
ed in the main-line circuit. 
The anvil or front contact 
of the key at each station 
connects by means of a 
^ wire with a battery, D, the 
opposite pole of the bat- 
M ter y being permanently 
united with the ground or 
return wire. When either key is pressed the distant 
bell will be rung. 







































ELECTRIC BELLS. 


297 


, 7 25 f Wh 7 at kmd °f hel1 signals are or have been employed on 
telephone lines f 

Agieat variety have from time to time been employed. 

Small, single-stroke bells were at first much used, 
and in their operation a steady battery was kept on the 
line, and the signals were given by breaking and closing 
the circuit a given number of times. Magneto-bells are 
more universally employed at present than any other, 
because they are much cleaner, more economical in the 

end, more easily managed, and very rarely get out of 
order. 

257 . What is a magneto-bell 1 

A magneto-bell is a polarized relay, having its arma¬ 
ture extended into a hammer which vibrates between 
two bells. 

It takes its name from the fact of its being operated 
by the electric pulsations produced by the rotation of 
coils of wire across the field ol* force of a magnet. 

258 . What is an individual signal-bell i 

Described in general terms, it is a bell which, when 
placed in series with other bells in an electric circuit, is 
-so arranged as to ring when desired, to the exclusion of 
the others. That is, if, for example, six stations were 
placed on one circuit, any one of the six may be signal¬ 
led without ringing the remainder of the bells in the cir¬ 
cuit. These bells are usually adapted to be rung ex¬ 
clusively from the central station ; but some varieties 
are capable of ringing any station from any other 
station. 

259 . Upon what principle are individual signals constructed 1 

Many different principles of action are embodied in 

these bells. A large number of them are operated by 
successive pulsations of electricity, which, when sent 
over the line, work a ratchet-wheel, either positively or 
by controlling the escapement of a clock-train. This 
ratchet-wheel, at a certain definite time or place, differ¬ 
ing at each station, either brings into activity an extra 
electro-magnet, which works the bell-liammer, or al- 


298 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

lows tlie bell-liammer to reach the bell at the required 
station ; the bells at the other stations having their 
electro-magnets cut out of circuit or their hammers me¬ 
chanically controlled. When brought to the ringing- 
point, bells of the step-by-step class are frequently 
caused to ring by sending a current of different cha¬ 
racter from that used to work the step-by-step motion. 
Other kinds of individual signals are worked by a clock- 
train, which at definite times introduces the different 
magneto-bell magnets into the circuit. In such appa¬ 
ratus the clock-work is tripped by an electric current 
sent from the central station, and rotates, bringing into 
circuit the different bells one after another. Still an¬ 
other kind is the harmonic ; these have armatures poised 
or tuned differently at each station in circuit. A trans¬ 
mitting instrument is placed at the central station, and 
provided with a circuit-breaker. The armature of the 
transmitter is adjustable in length, and when set in 
motion, only that circuit bell which corresponds in its 
rate of vibration to the rate of vibration of the circuit- 
breaker will ring. 


CHAPTER XXI. 


THE TELEPHONE. 

260 . What is the electric telephone f 

The idea expressed in the word telephone is the trans¬ 
mission of sound to a distance, and hence any instrument 
capable of such transmission is properly termed a tele¬ 
phone. The electric telephone, however, does not ac¬ 
tually transmit sound, but is simply an instrument by 
which, through the agency of electricity and a conduct¬ 
ing medium therefor, sounds of any kind, including 
articulate speech, when produced at any point or place, 
may be simultaneously reproduced at any other place at 
a distance therefrom. 

261 . What is the magneto-telephone % 

It is a telephone in which, when used as a transmit¬ 
ter, the vibrations of a metallic diaphragm, when sounds 
are uttered in its vicinity, cause variations of intensity 
in the field of force of a magnet, whereby electrical cur¬ 
rents corresponding in character and form to the origi¬ 
nal sounds are produced in a helix of insulated wire 
surrounding the pole or poles of the magnet; these tra¬ 
verse a line-wire in the circuit of which the helix is in¬ 
cluded ; and in which, when used as a receiver, the said 
currents circulating in the helix vary the strength of 
the magnet, which consequently attracts its diaphragm 
with varying strength, permitting it in turn to vibrate, 
and, by the movement in the air so caused, to repioduce 
similar sounds to those transmitted. The magneto-tele¬ 
phone is now used almost exclusively as a receiver, since 
it has been long known that battery telephones aie much 
powerful transmitters. It consists of a magnet, 

299 


more 


300 ELECTRICITY, MAGNETISM, AND TELEGRAPHY 


which may be either an electro or a permanent magnet. 
On one end of this magnet, or of a soft-iron core affixed 
thereto, is placed a coil or helix of fine, silk-covered 
wire, while stretched immediately in front of this core 
and coil is an elastic disc or diaphragm of thin sheet- 
iron, held to its frame by being compressed at its edges 
between t lie case and its cap or ear-piece. Some of the 
lines of force of the magnet pass through the coil, and 
others through the iron disc. Thus the plate is attract¬ 
ed towards the nugnet with a constant force when the 
instrument is quiescent. When, however, a constantly 
varying electric current is passed through the coil, in 
either direction, the strength of the magnet is momen- 
tarilv either increased or diminished, the attraction 
between it and the diaphragm varying accordingly. 
When the current in the coils is in such a direction as 
to reinforce the magnet the diaphragm is attracted more 
strongly than before, while if it is in the opposite direc¬ 
tion it is attracted less strongly. Now, as these varia¬ 
tions in the strength of the current are controlled by the 
action of the distant transmitter, they are in exact ac¬ 
cordance with the movements of its diaphragm, and 
thus the diaphragm of the receiving telephone is caused 
to vibrate also in accordance with the transmitter, and 
reproduces the sound. 

262 . Can the magneto-telephone , just described , transmit arti¬ 
culate speech , or is it restricted to its reproduction t 

It transmits speech quite distinctly ; indeed, for some 
time after its invention it was used for this purpose 
quite as much as for a receiver. It is one of the dis¬ 
tinctive features of the magneto-telephone that it may 
be so used. When acting as a transmitting telephone 
the operation of the instrument, depending upon the 
principles of magneto-electric induction, is as follows: 
The voice of the speaker throws the air into vibrations ; 
these, acting on the diaphragm, cause it also to vibrate ; 
every vibration of the diaphragm alters the magnetism of 
the inducing magnet, and at every change in the mag- 


THE TELEPHONE. 


301 


netic strength a transitory current is produced in the 
coil. Since the coil is in the line circuit, these transitory 
currents pass over the line and through the distant coil 
also. There they affect the magnetism of the receiving 
instrument in a similar way ; and the diaphragm of the 
said receiving instrument, being thus attracted with 



varying degrees of strength, repeats or reproduces the 
motions of the transmitting diaphragm, and the speech 
uttered in the mouth-piece of the sending telephone is 

thus duplicated by the receivei. 

263 . Is the magneto-telephone restricted to any particular 

No ; it may and lias been made in many forms. The 


























































302 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


standard form, which is that adopted by the American 
Bell Telephone Company, is shown in Figure 118, while 
Figure 119 is a vertical section of the same, showing the 
internal construction. It consists of a case of ebonite or 
hard rubber, containing a compound bar-magnet made 
of four separate bars of steel (each one separately mag¬ 
netized), laid together in pairs with similar poles to¬ 
gether. By this construction it is found that the mag¬ 
netism is more permanent than if a single bar were used. 

At each end, between the two pairs, is placed a soft- 
iron core or pole-piece. The shorter one is placed at the 
end intended for the handle, and a screw passes into it 



Fig. 120. 


from the outside of 
the case and aids 
in holding the parts 
together ; the long¬ 
er pole piece is 
placed at the dia¬ 
phragm end. 

The helix, which 
is formed of very 
fine silk-covered 
wire, surrounds this 
longer core, and 
ordinarily has a re¬ 
sistance of about 
seventy-five ohms : 

%j / 

its terminal wires 
are extended 
through the case 
beside the magnet, 


and are soldered to two binding-screws at the end of the 


handle. Stretched in front of the pole-piece is the dia¬ 
phragm, which is simply a thin, round iron plate, such 
as is used by photographers in the preparation of ferro¬ 
types. This is clamped at its edges between the end of 
the case and the cap which forms the ear-piece, and is 
thus maintained in close proximity to the magnet-core, 

























THE TELEPHONE. 


303 


which, however, it is never allowed to touch. This instru¬ 
ment is almost universally used in America. Another 
form which has been used considerably is that of the 
“Pony Crown,” of which Figure 120 shows a sectional, 
and Figure 121 a perspective, view. 

The “Crown Telephone,” represented in perspective 
by Figure 122, has also been used to some extent. 

The telephone designed by M. Clement Ader is one 
of the handsomest forms, and is used in France. It is 



Fig. 


121 . 


Fig. 122. 


shown in sectional elevation in Figure 123, while 
Figure 124 is a plan view of the magnetic cores and 
helices, with their enclosing cup, the diaphragm being 
removed, and Figure 125 a side elevation of the in¬ 
strument. 

In this telephone A is the magnet, which is made cir¬ 
cular. The pole-pieces are of rectangular form, and are 
surrounded by small helices or spools, B B, which in 
practice are connected with the binding-screws, N N, and 
by their means included in the line circuit. A cup of 
non-magnetic metal, O, is fastened to the magnet, and 
surrounds both helices, forming an interior space, across 
which, and passing close over the cores, is the dia- 

















































304 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

phragm, M. A cap, C, fitted with a flaring ear-piece* 
E, surmounts the instrument. The peculiar feature of 
the Ader telephone is what the inventor calls a rein¬ 
forcer. This is a mass of iron, X, enclosed in the cap, 
C, and lying within the field of force of the magnet, A, 
and said to aid and reinforce the magnet in its action on 
the diaphragm, and thus to cause the diaphragm to vi¬ 
brate more energetically than it otherwise would, and 
to give out louder articulations. Very satisfactory re¬ 
sults have been obtained from this instrument. 

It is useless to attempt a description of the num- 






berless forms of magneto-telephones which have been 
produced, the instrument being apparently capable of 
indefinite variation in form, but of very little variation 
in principle. 

264 . What is a battery telephone transmitter f 

It is an instrument adapted for the transmission of 
articulate speech, in which the operating electrical cur¬ 
rents, instead of being actually produced by the vibra¬ 
tions of a diaphragm in proximity to a magnet, as are 
those of the magneto-telephone, are developed by a vol¬ 
taic battery, and the vibrations of the diaphragm under 
the influence of the voice operate merely to control the 


























the telephone. 


305 


diluents so produced. Battery telephones have been 
commonly arranged in two classes—viz., those like the 
d^'Pmal Edison telephone, in which varying degrees of 
pressure are brought to bear upon certain semi-conduct- 
ing substances included in the battery circuit, whereby 
the paitides of such substances are brought into vary¬ 
ing degrees of intimacy, their resistance varying in a 
coiresponding degree and in proportion to the amount 
of pressure to which they are subjected; and those 
which are also technically and popularly called micro¬ 
phones, in which two points or electrodes of the circuit 


are brought more or less closely together in such a man¬ 
ner that the slightest shake or vibration greatly affects 
the amount of the resistance at the point of contact, and 
thus, of course, throughout the circuit. 


265 . How do such instruments operate when used to transmit 
articulate speech i 

In those of the former type a diaphragm is mounted 
in a frame, just as in the Bell telephone, and is arranged 
to press with a light but steady initial pressure against 
a little button of prepared carbon or lampblack which 
is placed in the circuit. The resistance of finely-di¬ 
vided carbon has been by some supposed to diminish 
greatly under pressure ; but the real cause of the ap¬ 
parent diminution is now thought to be, as before in¬ 
dicated, the closer intimacy into which the finely-di¬ 
vided particles are brought. However that may be, 
when the diaphragm is spoken against it vibrates, and 
presses with varying degrees of strength against the 
lampblack button, causing its resistance correspond¬ 
ingly to vary ; and as the electro-motive force is sup¬ 
posed to be constant, the strength of the current in the 
circuit varies inversely with the resistance of the but¬ 
ton. When the resistance of the button is greatest the 
strength of current is least, and when the resistance of 
the button is at its minimum the current strength is at 
its greatest. The best authorities no longer think that 
in the transmitter the resistance of the substance of the 


306 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


carbon is susceptible of variation, but believe that such 
variation is due, as we have already stated, to the vary¬ 
ing degree of con¬ 
tact between the 
multitude of par¬ 
ti c 1 e s composing 
the mass. 

The Edison trans¬ 
mitter, which is the 
best-known instru¬ 
ment of the forego¬ 
ing class, is shown 
in Figures 126,127, 
and 128 ; Figure 126 being a vertical section of the trans¬ 
mitter, Figure 127 a perspective view, and Figure 128 a 
view of the entire instrument mounted on a jointed arm 
and fitted on a desk-stand, with bell-call, and automatic 
switch operating by the removal and replacement of the 
receiving telephone 
to change the line 
from its normal route 
through the signal- 
bell to the branch 
leading through the 
telephone. 

Figures 127 and 128 
require no explana¬ 
tion. In Figure 126, 
which shows the 
transmitter in sec¬ 
tion, the button of 
prepared carbon is 
compressed between 
two metal surfaces, and the initial pressure is given by 
a screw, which is capable of adjustment from the rear. 
The diaphragm presses upon a protuberance of the 
upper metal plate, and when spoken against varies the 
contact between the metal plates and the button. One 



Fig. 127. 











































































































THE TELEPHONE. 


307 


of the circuit-wires is attached to the upper metal plate, 
and the other to the metal casine: 

dhe well-known Blake transmitter may be taken as 
the type of the second variety. Figure 129 represents 
the external appearance of this instrument as usually 
constructed. 

Ihe operative parts consist of a diaphragm loosely sup- 


Fig. 128. 



ported in a frame and clamped thereto, while suspend¬ 
ed from one of its edges are two hat springs; the nearest 
one to the diaphragm is the lightest of the two, and at 
its extremity carries a little stud of platinum, which at 
one side touches the diaphragm, and at the other a little 
disc of hard carbon with a highly polished face ; the 
carbon disc is carried on the lower end of the other 
and heavier spring. The two springs are relatively so 
adjusted that when they both from any reason are forced 



























































































308 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

away from tlie diaphragm, the platinum point has a 
tendency to follow the carbon disc for at least a short 
distance, usually about three-eighths of an inch. 

The springs are insulated from one another, and the 
only connection between them is at the point of contact 
between the platinum and the carbon. 

Figure 130 shows a sectional elevation of the working 

parts of the 
t r ansmitter. 
The two springs 
are carried upon 
the same adjust¬ 
ing lever, F, this 
being suspend¬ 
ed from the 
frame, B, by a 
still* Hat spring, 
and being ad¬ 
justable by the 
screw, G. This 
adjustment reg¬ 
ulates the ini¬ 
tial pressure of 
the carbon and 
platinum elec¬ 
trode, and also 
the pressure of both against the diaphragm, I). 

Figure 131 is a representation of the instrument with, 
the door open and all parts in their proper position. 
The diaphragm, which is insulated from the iron frame 
by an encircling band of india-rubber, is on one side 
clamped to its frame by the brass clamp, 7/, and is at 
the other furnished with a damping spring, K, by which 
undue vibrations are checked. 

The front of the case is fitted with a mouth piece; and 
in one corner of the case, as shown in Figure 131, the 
induction-coil stands* Connections are arranged where¬ 
by the two springs and the electrodes they carry, to- 




























































































































the telephone. 


309 


gether with the primary circuit of the induction-coil, 
aie placed in a battery circuit. These circuit con¬ 
nections are represented in Figure 132. A, B, C, and 
I) are binding screws, A and B for the battery-wires 
and C and D for the line-wires. Entering at A, the 
ciicuit of the battery proceeds by the wire S to the 
hinge TI, and by the wire M to the platinum electrode 
through the spring, I ; from thence 
it continues to the carbon button, 

J, and by the spring thereof to 
the metal adjusting-lever, K, and 
by means of the screw, O, to the 
frame, V. A wire, L, unites this 
frame to the lower hinge, G, and 
from thence another wire, P, leads 
to the primary coil, F, and out 
to the battery return by wire Y 
and screw B. The line-wires, or 
line and ground wires, are simply 
attached to the binding-screws C 
and D, which by the wires X and 
W lead through the secondary 
coil, E. In this diagram N re¬ 
presents the diaphragm. When in 
the operation of this transmitter 
the diaphragm is spoken to, the contact resistance of 
the platinum and carbon electrodes is varied, and the 
resistance of the circuit, and the strength of the current 
flowing therein, are correspondingly varied. 

The essential difference between the action of the bat¬ 
tery and magneto telephones, when the latter is used as 
a transmitter, is that in the battery transmitter the 
electrical undulations are produced by varying the 
resistance, and in the magneto by varying the elec¬ 
tro-motive force. 

266 . What is the reason that an induction-coil is used in 
connection with battery transmitters i 

It is found to be an advantage to use an induction-coil, 



































































310 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

and to place the microplionic contact, or the variable re¬ 
sistance, in its primary circuit, connecting the termi¬ 
nals of the secondary circuit of the coil with and in the 
line circuit, because although the said resistance is ca¬ 


pable of, and actually passes through, great variations 
when actuated by the vibrations of the diaphragm, 
the extreme variation between the highest and lowest 
points is but an inconsiderable factor in a long-line cir¬ 
cuit, whereas the same variation in a short local circuit 
is proportionately great. Therefore by placing the 










































































THE TELEPHONE. 


311 


variable lesistance in tlie short circuit of a primary 
©oil, where a comparatively small change in the total 
resistance in the circuit would cause a great difference 
in the strength of current; and by causing the second¬ 
ary coil to be a part of the line circuit, we produce 
in the secondary coil, and hence in the line of which 
it forms a part, induced currents, having as wide 



Fig. 132. 


a range of variation in the line circuit which they 
traverse as the battery currents which induce them 
have in the primary coil and circuit; and they thus act 
with equal vigor upon the diaphragms of all receiving 
telephones in the main circuit, irrespective of the vary¬ 
ing distances at which they may be placed. 

267 . What other types of transmitting telephone are used % 

There are but two other forms of transmitter that 
have been employed to any extent. These will be 
now described. 

The first is the Crossley transmitter, which is repre¬ 
sented by Figure 133, and consists of a number of varia- 





















312 ELECTRICITY, MAGNETISM, AND TELEGRAPHY 


ble contacts, which may be partly in series and partly 
in multiple arc. As usually constructed, these contacts 



are produced by arranging on a wooden diaphragm, 
which may or may not be furnished on the reverse side 
with a mouth-piece, a compound microphone, consisting 



of four carbon pencils resting loosely at their ends in 
carbon socket-blocks of the form shown. The circuit- 
wires are attached to two of the opposing socket-blocks, 


































































































THE TELEPHONE. 


313 


The microphone in practice is worked with a battery 
and fitted with an induction-coil, precisely as in the 
Blake and Edison transmitters. The entire apparatus 
is set up for work in the form represented in Figure 134. 

The apparatus is mainly enclosed in a compact box, 
on which is fixed the call-bell, N, a calling-key, E, be¬ 
ing placed on the front of the box, and the usual au¬ 
tomatic switch, adapted to operate as a rest for the tele¬ 
phone, at the end opposite to the bell. 

The second form is one wherein suitable conducting 
material in a finely-divided condition or in the form of 
a coarse powder is enclosed between two conducting 
surfaces in a battery circuit, the strength of currents 
being varied by the change of 
position in the particles of the 
powder. The principal type 
of this instrument is that 
invented by the Rev. Henry 
Hunnings, and of which Fig¬ 
ure 135 is a representation. 

A metal plate, B, of any desir¬ 
ed thickness, is placed in a re¬ 
cess cut into a suitable block, 

D, and connected with a bind¬ 
ing-screw terminal, E ; stretched 
over this, and held in place by 
a ring, F, or in other suitable 
way, is a very thin diaphragm 
of metal, A (platinum foil is 
generally used), which is ar¬ 
ranged at such a distance from 
the first plate as to form a shal¬ 
low intervening space. The thin 
diaphragm is connected with the 
second binding-screw, and the 
intervening space is nearly fill¬ 
ed with loose, finely-divided con¬ 
ducting . material, C, oven-made coke being found to 































314 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

give good results. The instrument, when in use, may be 
connected directly in the line circuit, a battery also being 
included therein, its great initial resistance rendering the 
use of an induction-coil unnecessary. Of course this 
transmitter is not restricted to any special form. In 
practice a suitable handle is usually added for con¬ 
venience. Both Crossley’s and Thinnings’ transmitters, 
though differing materially in detail from one another 
and from transmitters of the Blake and Edison types, 
yet operate on the broad principle of varying the 
strength of a battery current by varying the resistance 
of the circuit at one or more points in the said circuit. 

268. What is Dolbear’s receiving telephone i 

It is a receiver in which the vibrating plate is operated 
by the variation of a static charge of electricity instead 
of by the variation of magnetism produced by a varying 
current. 

The instrument in its simplest form is shown in sec¬ 
tion in the figure, and consists of two metallic discs, C 

and D, about two inches in 
diameter, so mounted as not 
to be in metallic contact. This 
is effected by separating them 
at the edges by a flange of 
hard rubber, which forms a 
part of the enclosing case. 
The mouth-piece is screwed 
down over one of the plates, 
and a handle over the other. 
Through the middle of the 
handle a screw is sunk, which 
touches the back plate and 
serves to adjust its flexibil¬ 
ity. The back plate is thus 
fastened both at the middle 
and at the edges, and therefore 
cannot vibrate, while the front 
plate, being fastened only at the edge, is free to vibrate. 










THE TELEPHONE. 


315 


A screw-post, A, is attached to each plate, by which 
the instrument may be attached to the line-wires or to 
the line and ground. It is quite feasible, however, to 
connect but one of the plates to a binding-screw termi¬ 
nal, foi attachment to the line-wire only, and to unite 
the other plate to a metal ring or plate on the knob 
which must be touched by the person using the instru¬ 
ment. A large induction coil is essential in connection 
with the transmitter when this receiver is used, and any 
microphonic transmitter will answer. 

269. H liy is it usual to place the receiving telephone , when 
not in use , upon a hook or yoke at the end of a lever- 
switch l 

Upon the introduction of the telephone as an instru¬ 
ment of electrical communication it was found that it 
could not be depended upon to speak loud enough to 
announce when a message was to be sent, and thus it 
became requisite to place at each station an electric bell, 
by means of which a signal might be given from the dis¬ 
tant station whenever it became desirable to attract at¬ 
tention. It was also found to be advantageous for many 
reasons to keep the telephone helices out of the line 
circuit, except during the act of conversation. A 
switch which should be able at any desired moment 
to cut the bell-magnet out from the line, and introduce 
the telephone into the line circuit, and vice versa , thus 
became an essential. A button-switch was first used for 
this purpose, but the attendant or user frequently for¬ 
got to replace the switch, so as to restore the signal-bell 
to the circuit when conversation was finished. This led 
to the device of a lever-switch which should be operated 
by the weight of the telephone ; and the fact that when 
the telephone was laid down the hook or yoke was the 
most natural place for any one to leave it, was relied 
upon to furnish a constant and sufficient reminder for 
persons so to place it, and thus make the required cir¬ 
cuit change automatically, or without any positive act 
of their own being necessary. 


316 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 



270. How is the automatic sic itch generally constructed ? 

A bar of metal, terminating at one end in a liook or 
yoke adapted for the support of a telephone, is pivoted 
in the bell-box, so that the end for the telephone sup¬ 
port projects some distance on the outside through a 
slot. This bar is permanently attached to the line-wire, 

and when the weight 
of the telephone is on 
the bar it is brought 
into contact with a 
flat metal spring 
which is united by 
a wire to the bell- 
magnet, and thence 
to earth. When the 
weight is taken from 
the end of the bar 
the outer end of the 
bar is drawn upward 
by a spring, and makes contact with another spring 
united with a wire leading to the telephones, and thence 
to the earth. The connections are shown in the dia¬ 
gram, Figure 137. 

271. In an ordinary magneto-hell box what other office is ordi¬ 
narily performed by 
the automatic switch f 

Since the general 
introduction of the 
battery transmit¬ 
ter, in addition to 
the work of trans¬ 
ferring the main¬ 
line connection 
from the signal-bell 
to the telephone 

branch, the auto- Fig - 138 - 

mafic switch-lever is so arranged as to close the local 
battery circuit of the transmitter when the telephone 


























































THE TELEPHONE. 


317 


is taken from its support. Owing to the general use of 
open-circuit batteries for this work such a contrivance 
is necessary. For convenience and compactness the 
battery circuit is led into the bell-box, and terminates 
therein in two flat springs, which, when the telephone 
rests upon its lever, have no communication with one 
another. Leaving the carbon pole of the battery, a wire 
may be led to the transmitter ; there the circuit is 
through the contact points and the primary circuit of 
the induction-coil; from the transmitter it goes to the 
bell-box to one of the fiat springs, while a wire from 
the other spring connects with the other pole of the 
battery. The act of removing the telephone from its 
place of rest, and the consequent recoil of the switch- 
lever, is made to interpose a metallic connecting piece 
between the two fiat springs, and so the circuit is closed. 


CHAPTER XXII. 


ELECTRO-THERAPEUTICS. 

272. What is meant by the compound term “electro-physi¬ 
ology ” % 

Electro-physiology is that branch of electrical science 
which treats of animal electricity and its laws ; and also 
of the phenomena produced by the action of electricity 
upon the skin, muscles, and other organs of liVing be¬ 
ings when in a natural or healthy condition. 

273. What effects may be produced in the body by the appli¬ 
cation of electricity i 

When a current from a battery of considerable elec¬ 
tro-motive force is passed through the human body it 
produces a disagreeable tingling or burning sensation at 
the points at which it enters and leaves the body. A 
sudden and strong current of short duration, such as 
would be produced by the discharge of a Leyden jar, 
when sent through the body, produces what is gene¬ 
rally known as an electric shock. The disturbance 
caused in the animal system by such shocks can be 
made so great as to produce severe illness, or even death. 
Deaths by lightning are due sometimes to the sudden 
discharge of electricity from the body, which has been 
inductively charged by the clouds, and sometimes to the 
direct stroke. 

The passage through the body of a rapid succession of 
magneto-currents, or of currents from an induction-coil, 
produces a species of temporary paralysis or numbness, 
so that a person grasping the electrodes connected with 
a source of electricity cannot let them go, but is con¬ 
strained to convulsively hold them until the cessation of 
the currents. 


318 


ELECTRO-THERAPEUTICS. 


319 


_ That many modifications may be made in the condi¬ 
tion of an animal body by electricity is very evident 
from the contraction of muscles and nerves when sub¬ 
jected to its action; and also from the fact that the 
Quids of % the body are all compounds of several ele¬ 
ments, and hence are all capable of electrolysis. 

274. II hat is the meaning of the words therapeutics and elec¬ 
tro-therapeutics f 

Therapeutics is the name of the science of healing. 
Electro-therapeutics is the branch of electrical science 
that treats of the study of electricity in its relation to 
disease and as applied to the healing or alleviation of 
disease. It is a very old idea; indeed, the remedial 
powers of electricity are referred to by Pliny. Only 
quite recently, however, has it advanced to the dignity 
of a science, and its practical history may be traced from 
the year 1743, when Kruger d’Helmstadt suggested that 
frictional electricity might be made serviceable in the 
practice of medicine. From that time until the dis¬ 
covery of the voltaic battery, fifty-six years later, fric¬ 
tional electricity was considerably used as a remedial 
agent, with varying success. In 1799 the voltaic battery 
was first constructed. This gave new life to electro-the¬ 
rapeutics, and rapidly superseded the use of frictional 
electricity ; and voltaic currents yet subserve valuable 
purposes in this department, and are extending their 
usefulness continually. Another advance was made in 
1832, when Neef, of Frankfort, commenced to use the 
rapidly alternating currents of magneto-electricity in 
the treatment of diseases. For a long time, however, 
electrical treatment was regarded as a species of quack¬ 
ery, but is now fully recognized as a valuable element 
in the healing art. 

Both battery and magneto currents are at the present 
time extensively employed in electro-therapeutics. 

275. What are the names applied by the medical profession 
to the three forms of electricity we have referred to f 

The first, frictional electricity, is often denominated 


320 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

Frariklinic , because of the large share borne by Frank¬ 
lin in its application to medicine. The second form is 
generally called Galvanic , and its application is called 
“electrization by galvanization,” because Galvani, the 
Italian physician, by his researches brought the subject 
prominently before the scientific world, which publicity 
resulted in the conception and construction of the bat¬ 
tery by Volta. The third form is by the medical pro¬ 
fession called Faradic electricity, because Faraday was 
the discoverer of magneto-currents and the method of 
producing them. 

276. What instrumentalities are principally employed in elec¬ 
tro-therapeutical applications f 

The direct current of a battery is sometimes employed 
through the intervention of a coil, which is composed 
of wire varying in thickness at different parts of its 
length, and furnished with a switch, by which more or 
less of the coil may be placed in circuit; a circuit- 
breaker is also provided, by which, if desirable, a suc¬ 
cession of shocks may be produced. Frequently 7 a com¬ 
plete induction-coil is employed, in which case the elec¬ 
trodes of the secondary coil are applied to the patient. 
Magneto-electric machines are also extensively used for 
medical purposes, and are very convenient for the ap¬ 
plication of rapidly recurring pulsations of alternating 
direction. 

277. TT7 lat is meant by electro-surgery ? 

It is a branch of electro-therapeutics which exclu¬ 
sively treats of the application of electricity to such 
diseases which are commonly known as surgical. In 
addition to the ordinary methods of application by 
passing electricity through the body or portions of the 
body, it includes two other methods— i.e ., galvano-cau- 
tery and electrolysis, which two are peculiar to it. 

Electro-surgery as a special branch dates back only 
as far as 1825, but is, perhaps, now the most valuable 
feature in the entire field of electro-therapeutics. 

Galvano-cautery means the practice of burning or 


ELECTRO-THERAPEUTICS. 


321 


searing by a wire of high electrical resistance, heated 
by the passage of electricity through it. This method 
is often used in the removal of tumors and cancers. 
Electrolysis, which implies the art or process of de¬ 
composing a compound substance by electricity, is 
chiefly applied to the decomposition of morbid growths, 
or to organs affected by chronic inflammation, by 
means of some form of needle electrodes, which are 
inserted in the diseased part. 

278. What is the approximate electrical resistance of the hu¬ 
man body i 

Hie resistance, in ohms, of the human body averages 
about as follows : From one hand to the other, through 
the body, hands dry, over ten thousand ohms ; same 
with hands wet, six thousand ohms. 

From mouth to hand, hands dry, eight thousand 
ohms ; same 'with hands wet, live thousand ohms. 

- These results were deduced from measurements 
made of eight persons by Professor A. E. Dolbear, of 
Tufts College, Somerville, Mass. 

279. What is an electrical probe t 

The electrical explorer, or probe, is a little instru¬ 
ment employed to ascertain the presence and location 
of metallic bodies in wounds. 

It is in shape much like the Edison electric pen, and 
consists of a slender rod or sound, which encloses two 
conducting wires or needles, insulated from one another, 
and covered entirely by a non-conducting substance. 

The points are uncovered, and the other or outer end 
of the sound supports in a convenient stand a little vi¬ 
brator, or trembling electro-magnet. One of the probe 
conductors is attached to the electro-magnet, and the 
other by a flexible cord to the battery direct; the other 
pole of the battery is connected with the second magnet- 
wire. When the circuit is closed by the contact of the 
two probe-points upon a metal surface—for example, a 
leaden bullet—the battery current traverses the magnet, 
causing the armature to tremble. The depth at which 



322 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

the bullet lies is simultaneously made known by the ex¬ 
tent of insertion. 

The first electric exploration of wounds occurred in 
1863, and was conducted substantially upon the above 
principle; instead, however, of the vibrating magnet a 
galvanometer was used as an indicator. 




CHAPTER XXIII. 

OTHER APPLICATIONS OF ELECTRICITY:—ELECTRIC CLOCKS 

TIME-BALLS—ALARMS—BLASTING—TRANSMISSION OF 

POWER—ELECTRICAL STORAGE. 

280. What are electric clocks t 

They are clocks which are either driven or controlled 
by electricity. In clocks which are driven by electricity 
the ordinary nse of a spring or weight is dispensed 
with ; and instead of using the pendulum to retard 
and regulate the motion, it is employed to propel the 
hands, being itself attracted alternately from side to 
side. The second class of electric clocks is that in 
which a clock of otherwise ordinary character, driven 
by weight, controls or governs by electricity a number 
of subordinate clocks. 

A clock of the former class consists, usually, simply 
of a pair of hands adapted to rotate round a dial, and 
placed on the axis of a ratchet-wheel, which, by means 
of an electro-magnet, armature, and pawls, is caused to 
advance one tooth with every two swings of the pen¬ 
dulum. 

Clocks of the second class, on the contrary, are gene¬ 
rally constructed with a regular train of clock-work, the 
escapement of which is alternately released and retained 
by an electro magnet, which is charged and discharged by 
the action of the controlling clock, which makes and 
breaks the circuit of the said electro-magnet. 

281. When and by idiom were electric clocks of the first 
variety invented t 

The clock in which electricity supplies the actual 
motive power was first suggested by Alexander Bain in 

323 


324 ELECTRICITY, MAGNETISM, AND TELEGRAPHY'. 


the year 1840. In the next year, 1841, he, in conjunction 
with a Mr. Barwise, obtained a patent for the application 
of electricity to the regulation and movement of clocks. 
The patent specified for its principal object the move¬ 
ment of several clocks by currents of electricity, trans¬ 
mitted at regular intervals by the agency of a clock of 
ordinary character, which, of course, indicates the second 
system we have spoken of; and it is probable that Mr. 
Bain would have succeeded better had he carried out that 
system. But by a subsequent improvement each clock 
was made to move independently by electricity, and this 
method was at that time regarded as a much more perfect 
invention. 

The arrangement by which this is accomplished will 
be understood by reference to the annexed figure. The 

pendulum-bob, A, consists of a 
hollow coil of covered copper wire, 
and is suspended from the rod B, 
the wires, eel , from the ends of the 
coil, being carried up the pendu¬ 
lum-rod, and at the upper end 
thereof maintained in metallic con¬ 
nection with two springs from 
which the rod hangs. A brass 
tube, C, about two inches in diam¬ 
eter, passes through the coil, there 
being sufficient space left for the 
coil to move backward and for¬ 
ward without touching. Within 
this tube, and on each side of it, 
are placed permanent bar mag¬ 
nets, with their similar poles, n ri, presented towards one 


B 



another at a distance of about four inches apart. 

When an electric current passes through the coil, A, it 
instantly becomes magnetic ; the end towards the right, 
we will suppose, having a south polarity, and that 
towards the left a north polarity. The coil is conse¬ 
quently attracted towards the right, and is repelled by 



















































OTHER APPLICATIONS OF ELECTRICITY. 


325 


the magnets on the left, as the pendulum swings in that 
direction. 

Before arriving at the end of its vibration the connec¬ 
tion with the battery is broken by the action of the 
pendulum; the magnetic property of the coil instantly 
ceases, and it descends by the force of gravity. On as¬ 
cending the other arc of its vibration, contact is made 
with the battery, and a current is sent through the coil, 
but in the reverse direction; so that the left hand of the 
coil has south polarity given to it, and the right becomes 
the north pole. By this reversal of the current the coil 
is impelled towards the left, and the vibrations of the 
pendulum are thus maintained for an indefinite time. A 
light frame attached to the upper end of the pendulum- 
rod carries springs which connect with the coil-wires, e 
d, and make and break the battery contacts, and reverse 
the direction of the current through the coil. 

Fig;. 140 shows the mode in which the vibrations of the 
pendulum are made to propel the hands. An electro¬ 
magnet, A, is fixed on 
the top of the clock, and 
the current is sent 
through the coil on encli 
vibration of the pendu¬ 
lum. Upon each electri¬ 
cal pulsation the magnet 
attracts the armature, 

B, to which the pawl, I), 
is attached, and this, 
engaging with the teeth 
of the ratchet-wheel, E, 
advances it one tooth. 

The wheel is prevented 
from falling back by the retaining pawl, L. By this 
arrangement the ratchet-wheel is advanced one tooth by 
two swings of the pendulum. Thus vlien the wheel 
contains thirty teeth, and the pendulum vibrates once a 
second, the wheel will make one complete revolution 



Fig. 140. 


































326 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

every minute. That wheel will, therefore, constitute the 
seconds-wlieel of the clock, and the minute and hour 
hands may be moved by it in the same manner as in 
ordinary clocks. 

Mr. Bain worked these clocks by means of an earth 
battery consisting of a large plate of zinc and a quantity 
of coke buried in moist ground. They did not work very 
satisfactorily, chiefly, no doubt, because of the unstable 
nature of the battery. 

282. How may clocks of the character described above be 
governed by a central clock , arid by whom was such a method 
devised f 

As we have seen, Mr. Bain described such a system in 
his patent of 1841. Wheatstone, however, is generally 
regarded as the flrst person to conceive the idea of a 
number of clocks governed or controlled by a central 
clock. His ideas were greatly improved by Mr. R. L. 
Jones, an English railroad man, and Mr. Ritchie, of 
Edinburgh. Clocks operated upon this general plan 
have had considerable success, and are largely used in 
connection with observatories and many other large 
establishments. 

Mr. Jones used clocks made on the Bain principle. 
The standard or governing clock is the only one provided 
with a circuit breaker or changer, and its pendulum is 
not under electrical control. In short, it is of the usual 
construction, except that it is made to operate a circuit- 
breaker. 

The pendulums of the copying clocks have no break, 
as the primary pendulum performs the circuit-breaking 
function for all. 

The clocks are, therefore, necessarily maintained to¬ 
gether. The pendulums are not entrusted completely to 
the stimulus of the electricity, but are moved by their 
own weights, so that even if their supply of electricity 
should fail they would go on for a time without it. 
There is no conflict between the two controlling forces 
of electricity and gravity, and by this system, therefore,. 


OTHER APPLICATIONS OF ELECTRICITY. 327 

copying clocks of little value may be made as perfect 
as the most costly observatory clock. 

283. How are clocks of the second variety to be operated , and 
by whom were they first arranged f 

As already indicated, these clocks may have a regular 

train of mechanism, and may be operated, as shown in 

the annexed ligure, by an electro-magnetic escapement. 

One pendulum may serve any number of clocks. At 


each clock is an electro-magnet, B, the armature of 
which is a permanent bar magnet, N S, carrying an es¬ 
capement, D, which works into an escapement-wheel, E, 
and thus either positively propels the clock or regulates 
its movements. The pendulum may be placed in one of 
the clocks, and by dropping its points, A, into the mer¬ 
cury-cups, m', alternately, continually reverses the cur¬ 
rent of the battery, ZC, through the escapement magnet, 
B. Any number of these magnets may be worked in 
series by a proper proportionment of the battery. 

The first introduction of this principle into electric 
horology was made by a Mr. Shepherd, of London, who 
exhibited the arrangement publicly at the International 
Exhibition of 1851. 










































































328 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

284. How may time-balls and time-guns be operated i 
They are operated by being electrically connected 

with a clock which is arranged to 
complete a circuit by means of con¬ 
tact-springs, and thus at any pre¬ 
determined time attract the arma¬ 
ture of an electro-magnet and re¬ 
lease a trigger, which permits the 
ball to drop or lires the gun. The 
method will be understood on an 
examination of the annexed figure, 
142. A time-ball is usually a large 
wicker globe covered with painted 
canvas or flannel; this is fixed to a 
piston which falls down into a bell- 
mouthed tube just air-tight enough 
for the air to act as an elastic cush¬ 
ion. It is hauled up by hand a few 
minutes before the time at which it 
is to be dropped. 

2S5. How can ordinary clocks be made 
to ring bells at any desired time % 

There are several ways of doing 
this. One of the easiest is to place 
on the arbor of the hour-hand a cir¬ 
cuit-wheel of non-conducting mate- 
rial having a small piece of metal let in at one point of 
its periphery and extending through to the metal of 
the arbor, so as to be electrically connected with the 
frame and works of the clock. 

The wheel is made to fit, by friction only, upon the 
arbor, and is just tight enough to. prevent slipping, 
while it is sufficiently loose to be easily moved round 
for setting at any desired point. A fiat spring is attach¬ 
ed to an insulated base and made to press lightly on the 
edge of the circuit-wheel; it is connected with one pole 
of a battery. The metal part of the circuit-wheel, by 
means of the frame and clock-work and a connecting 
































329 


OTHER APPLICATIONS OF ELECTRICITY. 

wire, is united to one binding-screw of the alarm-bell, 
and the other screw of the bell to the second pole of the 
battery. When, by the movement of the clock, the 
spring is brought into contact with the metal piece on 
the edge of the circuit-wheel, the circuit is closed and 
the bell rings until the metal lias passed from under the 
spring. The wheel, being only attached to the arbor by 
friction, is easily readjusted. 

Sometimes an arrangement like the above is unsatis¬ 
factory, because the wheel, being on the hour-hand 
arbor, rings the bell too long ; when such is the case a 
second circuit-closer is attached to the arbor of the 
minute-hand, which closes the battery circuit at that 
point once an hour. But as the circuit is also open on 
the hour-hand wheel, the bell cannot ring • therefore 
only when both circuit-closers close at the same time 
can the bell ring, and only for the length of time that 
the wheel on the minute-hand arbor takes to pass its 
spring, which time can be made very short. 

Another way is to insert one or more metal points in 
the face or dial of the clock, connecting all the points to 
one of the bell and battery wires, and then to arrange a 
trailing spring to travel round, attached by friction to 
the hour-hand arbor, and connected with the other bat¬ 
tery wire ; a little switch is provided in each of the 
wires leading from the metal points to their main con¬ 
necting wire, and the switch of the point at which the 
bell is desired to ring is closed. 

286. What are the principal methods of blasting by electricity f 

Passing a spark discharge, produced either from a 
frictional machine or a Rulimkorff or Ritchie coil, 
through a fuse of fulminating powder, which in its 
deflagration kindles the larger charge of gunpowder 
or other explosive, is one very general method. 

Another way frequently adopted is to arrange a fuse 
in which a very fine platinum wire is joined in circuit 
with a pair of stout conducting wires leading from a 
battery. This wire becomes heated when the current 


330 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

flows, and, being laid amidst an easily combustible sub¬ 
stance, the latter is ignited and sets fire to the charge. 

287. Describe more particularly how frictional or high-tension 
electricity , such as that developed by the f rictional machine or 
induction-coil , is used to explode charges. 

A fuse is made, consisting of a hollow rod of gutta¬ 
percha or some other suitable non-conductor, and in 
this are placed two insulated wires with their ends 
bared; one of these wires enters the non-conducting 
rod at one end, and the other wire enters the other end, 
so that their bared ends tend to meet one another. 
These ends are not permitted to touch, but remain a 
little distance apart; they are, however, connected by a 
layer of the fulminating material or mixture, which is 
preferably a composition of sub-sulphide of copper, 
sub phosphide of copper, and chlorate of potash. A 
fuse has been employed which is based upon the action 
which india-rubber has upon copper. It has been as¬ 
certained that when copper wire is insulated with vul¬ 
canized india-rubber its surface becomes covered, after 
a lapse of some months, with a layer of sulphide of 
copper, which is capable of conducting electricity. The 
fuse is ingeniously formed by removing a portion of the 
covering from a loop of such wire, as in Figure 143, and 
then cutting away a very small piece of the wire. 



Fig. 143. 


A and B represent the wires leading from the source of 
the electricity, and the current, interrupted by the space 
between the points a and b, takes the route by means of 
the sulphide of copper which coats the inner surface of 
the covering, igniting it, and with it any inflammable 



OTHER APPLICATIONS OF ELECTRICITY. 


331 


substance, like gunpowder or gun-cotton, which may be 
placed in the cavity. 

If the exploding is done by an electric machine it is 
better to tirst charge a condenser by means of the ma¬ 
chine, and then discharge the condenser through the 
fuse. In addition to the sources of electricity which 
have been already mentioned— i. e ., the electric machine 
and induction-coil—a magneto-electric machine is fre- 
quently used ; while if the fuse employed is composed 
of the three ingredients tirst described it is quite possi¬ 
ble to explode it even with a battery current. 


288. Describe more particularly how electricity generated by a 
battery or dynamo-electric machine is used in blasting. 

The battery or dynamo-machine being provided, wires 
are led from its poles to the different points at which 
the explosions are to be produced. At these points the 
large wire, which is insulated, is cut, and a small piece of 
very fine platinum wire stretched between the two ends 
of the break. As many of these platinum joints as are 
desired are in this way placed in the circuit. The fuse 
is caused to surround the fine wire, which should be 
coated with fulminate of mercury. Upon closing the 
circuit of the 
battery or ma¬ 
chine the fine 
wires are heat¬ 
ed to redness 
by the passing 
electricity, and 
explode their 
charges. 

In the accom¬ 
panying figure 
the circuits are 

represented as - pig 144 

being arranged 

to operate the exploder from a safe distance. The fuse, 
being hidden in a hole drilled in the rocks, is connected 























332 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


by wires, a &, with a battery, B, the circuit of this 
battery passing also through the contact-points of the 
relay, R. The relay electro-magnet is in the circuit of 
the battery L, by means of the wires x y, and when the 
main circuit is closed by the depression of the key, Jc , 
the relay armature is attracted, the local points come 
together, the local circuit is closed, and the charge is 
fired. The battery B and relay, R, are, of course, 
placed in a protected position. 

289. What advantage has the second plan over the first % 

It has two advantages : first, that the condition of the 
conductors may be tested after they are laid, from time 
to time, as frequently as may be desirable, by feeble 
currents which will not heat the platinum wires to any 
great extent ; and, second, that several insulated con¬ 
ductors may be laid in one cable without interfering 
with each other, which cannot be done when a fuse is 
fired from a condenser discharge, owing to the powerful 
currents induced in the adjacent wires, which would fire 
the fuses attached to all the wires whenever an electri¬ 
cal current or impulse was passed along a single wire. 

290. Has electricity been applied to the production of motion f 

Yes ; the idea of a moving force derived from electri¬ 
city, and especially through the medium of electro mag¬ 
netism, was one of the earliest in the history of electri¬ 
cal science. 

Yumberless attempts have been made to embody the 
idea in a practical form ; nearly all of them, up to the 
year 1872, being based upon one principle—namely, 
the instantaneous production and destruction of force 
either by making and breaking the circuit of a battery 
which includes one or more electro magnets, or by re¬ 
versing continuously the currents in the circuit and 
through the electro-magnets. 

One of the earliest electro-motors of which we have 
any knowledge is that of Professor Jacobi, who in 
1834, under the auspices of the Russian government, 
constructed an electro-magnetic engine of considerable. 


OTHER APPLICATIONS OF ELECTRICITY. 


333 


power. This was fitted in a boat 28 feet long, 7J- wide, 
and dial ing 2f feet of water. The boat moved, when 
propelled by the engine, at a rate of four or five miles 
per hour. A battery of sixty-four cells was used to 
excite the engine. Some years later an electric engine 
was built by a Mr. Davidson, in Scotland, and tried 
on the Edinburgh and Glasgow Railway, but no great 
power was developed by it. 

One reason why these engines developed so little 
power is the very limited sphere of magnetic attrac¬ 
tion, and in order to overcome this disadvantage engines 



ton Page, contrived a g 
one of the simplest is sb 


with axial magnets, or suck¬ 
ing-coils, were devised. In 
these a core of soft iron is 
drawn alternately into and 
out of a hollow coil as the 
circuit is made and broken, 
and the reciprocating recti¬ 
linear motion thus produced 
is transformed into a regu¬ 
lar circular or rotary motion 
by a connecting-rod, a crank, 
and a fly-wheel. Our own 
countryman, Charles Graf- 
rp many such engines ; and 
wn in the engraving, Figure 


145. 


M. Froment, of France, has made one of the best of 
this class of motors. Figure 146 represents this ma¬ 
chine. It is made on the same principle as those already 
described—that is, the successive break and make of 
the current through the several electro-magnets. These 
magnets, A, B, C, and D, are four in number, and are 
fastened on an iron frame, X. A drum carrying eight 
soft-iron armatures, M M, rotates between the electro¬ 
magnets. The battery current enters at the screw-post, 
K, passes through the machine, and leaves at the sec¬ 
ond terminal, H. The current is broken, and each 
























334 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

magnet neutralized, just as the armature comes oppo¬ 
site to its poles; the magnetic power being restored at 
the moment when eacli armature lias passed one-half 
the distance which separates each electro-magnet from 
the next. These changes are made by a suitable circuit- 
breaker arranged on the metal arc, O. In the figure this 



Fig. 146. 


motor is represented as supplying power to turn a small 
mill. 

291. Have such electro-magnetic motors been practically suc¬ 
cessful t 

No ; several reasons have prevented this. In the first 
place, it is a physical impossibility for power derived 
from the consumption of zinc and acids in a voltaic bat- 










































































335 


01 HEM APPLICATIONS OF ELECTRICITY. 

tery to compete economically with power derived from 
the consumption of coal to produce steam. The con¬ 
sumption of the metal at the circuit-breaking points is 
also very rapid, necessitating close attention and militat- 
tng against satisfactory work. Moreover, the power in 
such engines operates under great disadvantages, and 
the transformation of electro-magnetism into mechani¬ 
cal eneigy is attended with great loss, chiefly owing, as 
before indicated, to the fact of the rapid diminution of 
the attiactrve power of the magnet as the armature re¬ 
cedes from it, the said attraction varying inversely as 
the square of the distance. 

# Some years since the late Dr. Joule published his bril¬ 
liant researches, in which he showed that the potential 
energy of zinc was so much lower than that of coal that 
it was impossible that a motor driven by the consump¬ 
tion of the former substance could ever successfully 
compete with steam, except in certain special cases 
where the pow T er required is very light. 

292. On what principle may practical electro-motors he con¬ 
structed t 

The only practical electro-motor known, and one 
which promises at no distant date to be eminently use¬ 
ful, is the dynamo-electric machine when made opera¬ 
tive by passing a current into it from some external 
source. It was not known until about the year 1872 
that the action of the dynamo-electric machine was 
reversible, and that it could be used interchangeably 
as a machine to develop electricity or as a machine to 
transform electricity into motion. 

M. Gramme early discovered that his machine could 
be so utilized; and it is said that the late eminent philo¬ 
sopher, mathematician, and electrician, Professor J. Clerk 
Maxwell, was so impressed with the far-reaching im¬ 
portance of this discovery that when asked what he 
regarded as the greatest discovery of the nineteenth 
century, he replied without hesitation, “The reversi¬ 
bility of the Gramme machine.” 


336 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

293. How are dynamo-electric machines arranged to operate 
as motors, and how may power by their agency be transmitted i 

Power from any convenient source, such as a steam- 
engine or water-wheel, is caused to drive one dynamo- 
electric machine, a belt being carried from the motor to 
the armature-pulley of the machine, and the armature 
is thus rotated. The rotation of the armature between 
the magnet-poles develops electric currents in its coils, 
which, if led away by conducting wires connecting at 
their distant extremities with the terminals of a second 
dynamo-electric machine, cause the armature of the 
second machine to rotate rapidly in the opposite di¬ 
rection to that of the first ; a pulley may be placed on 
the armature-shaft of the second machine, to which a 
belt is attached to convey the power thus reproduced 
wherever it is wanted. 

The first machine thus generates the current, which is 
utilized in imparting motion to the second machine. 

The work done by the original power is in the first 
machine transformed into electricity, and can then be 
conveyed or transferred by conducting wires to the dif¬ 
ferent points where it is required; arriving at such 
points, it is passed through the armature and field-mag¬ 
net coils of other machines, causing the armatures to ro¬ 
tate and to reconvert the electricity into motive power, 
which by any well-known means may then accomplish 
its work. 

As much as sixty per cent, of the original power has 
in this manner been experimentally reclaimed under 
favorable circumstances ; or, in other words, the pulley 
of the second machine has been known to exercise a 
power equal to sixty per cent, of the original power re¬ 
quired to work the armature of the first or generating 
machine. 

Practically this percentage is higher than can ordi¬ 
narily be expected ; for inasmuch as the armatures of 
all magneto or dynamo-electric machines generate cur¬ 
rents when rotated, there can be no exception in this 


OTHER APPLICATIONS OE ELECTRICITY. 


337 


case, and as soon as the armature of the second machine 
commences to revolve it sets up a current opposite in 
direction and consequently tending to weaken the origi¬ 
nal current and to reduce its power on the second arma- 
tare materially. 

294. Has electrical power so transmitted been utilized to any 
great extent t If so , where and how f 

ilie general utilization of this important application 
of electricity is still in the future. It has, however, 
been extensively illustrated upon the lecture platform, 
and was also practically illustrated in France in 1879, 
when two French engineers ploughed a field by power 
electrically transmitted. A double-ended plough was 
used, so that it might go either backward or forward 
without turning, like a ferryboat. This plough was 
pulled across the field from side to side by a pair of dy¬ 
namo-electric machines, one on each side. Both of the 
machines were driven alternately by electric currents 
supplied alternately to each by a third machine located 
upon the road a few hundred yards away, to which 
motion was given by a steam-engine placed near it. 

One of the most interesting and important features of 
the subject of electro-motion is the bearing which it 
has upon the railway problem. In all probability the 
present century will see a large proportion of the steam- 
locomotives of the present day superseded by dynamo- 
electric locomotives. The idea of applying electro-mo¬ 
tors to railways appears to have originated with Dr. 
Werner Siemens in 1867, although not until some years 
later did he find an opportunity to experiment practi¬ 
cally upon the subject. The first practical demonstra¬ 
tion of the idea was a small railway constructed by Dr. 
Siemens and exhibited in Berlin in 1879. This railway 
was circular and had a total length of about three hun¬ 
dred and fifty yards. The currents, from low-tension 
dynamo-machines, were transmitted along the rails and 
supplied to an electro-motor on the first car of the train 
by means of frictional contacts, such as metal brushes 


338 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


depending from the motor terminals and bearing upon 
the rails. This experimental railway was succeeded by 
a second, which was built by Siemens and Halske, and 
which was opened for business in 1881. This railway 
was tirst built from Berlin to Licliterfelde, but has since 
been extended to Potsdam, a distance of seventeen miles, 
and is now in process of a still further extension to Steg- 
litz. It works very successfully. It was found, in the 
light of experience gained by the Berlin railway, that 
instead of having a special locomotive it was better to 
attach a smaller motor to each car, which is now done. 

Mr. Thomas A. Edison lias also constructed an electric 
railway upon similar principles at Menlo Park, New 
Jersey, which he has operated for some time. It is 
stated that he has achieved a speed of thirty miles per 
hour. 

The latest experiments in the electrical transmission 

of power were made by M. Marcel Deprez quite recently 

in the workshops of the Northern Railway at Paris. 

These experiments consisted in the transmission of six 

horse-power over a line of wire twelve and a half miles 

long, via Bourget, and of ten horse-power over a twenty- 

two-mile line via Sevran Livrv. It is stated that the re- 

«/ 

suits were a reclamation of one half the original power 
in both cases. 

The data of the shorter-line experiment were as fol¬ 
lows : 

Resistance of the telegraph-wire, 160 ohms. 

Generator . 

Resistance of inducing armatures, 20 ohms. 

Resistance of field-magnet helices, 36 ohms. 

Number of revolutions per minute, 650. 

Strength of current, 2.1 amperes. 

Receiver. 

Resistance of armature-coils, 50 ohms. 

Resistance of field-magnets, 33 ohms. 


OTHER APPLICATIONS OF ELECTRICITY. 


339 


Number of revolutions per minute, 313. 

* Resistance of the total circuit, 299 ohms. 

Useful work measured on the brake, per second, 156 
kilogrammetres. 

The measurements of the electro-motive force and the 
mechanical work expended are not given. No satis¬ 
factory opinion can be based upon the above data as to 
the economy of the work done, especially as it has been 
ascertained that instead of working the generating ma¬ 
chine from an independent source of power which could 
be measured by a dynamometer, the power was taken 
from a countershaft in the shops, so that the horse¬ 
power expended could not be measured. Moreover, the 
generating and reproducing machines were placed very 
near to one another, and, though connected on one side 
by the line-wire 12J miles long, were connected for 
the return circuit simply by an insulated wire of a 
few yards in length. Therefore this was not a satis¬ 
factory practical test; and although the newspaper re¬ 
ports were very flattering indeed, and although the 
friends of M. Deprez claimed a return of 50 per cent., 
it is not easy to see how such conclusions can be arrived 
at from the incomplete data given. 

These experiments were not the first made by Marcel 
Deprez. In October, 1882, lie transmitted power with a 
certain degree of success between Munich and Mies- 
bach, a distance of a little over 31 miles. At that time 
it was broadly stated by the friends of M. Deprez that 
60 per cent, of the power expended was reclaimed ; but 
the certificate of the Munich Electro-Technical Com¬ 
mittee gives no more than 38.9 tier cent., even this being 
a liberal estimate. In this case also, although the re¬ 
turn of horse-power is stated at 0.25, no mention is 

made of the power expended. 

It thus appears that the only practical knowledge 
gained from these tests is the knowledge that it is pos¬ 
sible to transmit to a distance of at least thirty miles 


340 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


the force of a certain number of liorse-power over an 
ordinary telegraph-wire and by means of dynamo* 
electric machines. 

295. What are secondary batteries f 

Secondary batteries, frequently but erroneously called 
accumulators of electricity, are batteries which origi¬ 
nally have no electro-motive force of their own, but are 
capable of being acted upon by an external source of 
electricity in such a manner that they acquire the 
power to give out an electric current opposite in di¬ 
rection to that of the external source by which they 
were treated. Secondary cells consist of two plates, of 
identical material or character, immersed in some suit¬ 
able liquid, such as water. Normally such a cell can 
have no electro-motive force, because as the plates are 
alike and immersed in the same liquid there is no 
difference of potential between them, and consequently 
no E. M. F. and no tendency to set up a current of 
electricity. But if we connect such a cell in circuit 
with an active voltaic battery or a dynamo-electric ma¬ 
chine, or, in fact, with any other generator of strong 
and constant direct currents, a result occurs which we 
may regard as the storage of electrical energy. It has 
been found that if the immersed plates are made of lead 
the secondary effects are more powerful and lasting 
than if other metals are used ; therefore it has become 
customary to employ leaden plates in these batteries. 
Moreover, since it is well known that acidulated water 
has a much higher conductivity than pure water, and 
also aids the action of the charging current, it is usually 
employed as the liquid in which the plates are im¬ 
mersed. When the cell of leaden plates immersed in 
water acidulated with sulphuric acid is subjected to 
the action of the charging source, that plate which is 
connected with its positive pole, or, in other words, that 
plate of the secondary cell at which the current from 
the charging source enters, becomes covered with a 
spongy brown surface of peroxide of lead, while the 


OTHER 


APPLICATIONS 


OP ELECTRICITY. 


341 


-, er l )late 18 deoxidized by the liberation of hydrogen 

k™ le “ ute acld ; Wllen the leaden plates arrive at 
tins condition the battery is said to be charged, and 

m s to furnish an electrical current, as already stated, 
opposition to that of the charging current. If the 
original generator is now removed, and the wires lead¬ 
ing from the two electrodes of the secondary cell are 
connected together by a conducting wire, so as to form 
a closed circuit, it will be found that a current of elec¬ 
tricity will pass through it from the peroxidized plate 
to the other, the bright or deoxidized plate becom- 
mg gradually oxidized, and the oxidized surface of the 
other becoming gradually reduced to a less oxidized con¬ 
dition ; and the current will continue to flow until the 
two leaden plates are again brought to a similar con¬ 
dition. This identical phenomenon operates in nearly 
all voltaic batteries to coat their own plates with the 

gases oxygen and hydrogen, and is called “polarization 
of plates.” 


^96. Give a short account of the history of the secondary cell. 

The history of the secondary cell dates from the year 
1801. Gautherot, in that year, found that the wires of 
platinum or of silver, which had been employed as elec¬ 
trodes of a voltaic battery in the decomposition of salt 
water, acquired, and retained after they were discon¬ 
nected from the battery, the power of yielding a tran¬ 
sient current; this was, of. course, due to polarization. 
In 1803 a philosopher of Jena, Ritter by name, observed , 
the same phenomenon, using wires of gold ; and, attach¬ 
ing some importance thereto, constructed the first sec¬ 
ondary pile, which, like the pile of Yolta, was an actual 
pile of discs, consisting of alternating discs of copper 
and moistened card, piled one upon another, and moist¬ 
ened with a solution of salt or sal-ammoniac. 

It was found that this pile, after being connected for 
some time in the circuit of an ordinary voltaic battery, 
received a charge which was capable of giving a con¬ 
siderable shock. Ritter, however, did not succeed in 


I 


342 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

discovering tlie underlying principle of this phenome¬ 
non, and the only result accruing from his experiments 
seems to have been that they attracted the attention of 
other experimenters. In 1842 Professor Grove con¬ 
structed his gas-battery, which was a true secondary 
battery, in which the secondary currents were produced 
by the recombination of oxygen and hydrogen, previ¬ 
ously separated, by electricity derived from an external 
source. M. Gaston Plante, as early as 1859, followed 
up these researches by vigorous and persevering experi¬ 
ments, and succeeded in producing a really valuable and 
practical secondary battery, which has been utilized for 
a variety of purposes : it has been made to produce 
light; it lias been extensively employed in galvano-cau¬ 
tery and other surgical applications, in telegraphy, and 
even as a propelling power for velocipedes and pleasure- 
boats. Undoubtedly the present state of the electrical 
storage of energy, and our present knowledge of second¬ 
ary cells, is due more to M. Plante than to any other 
person. No advance was made upon the battery of 
Plante until quite recently. In the spring of 1881 it 
was announced that u a box of electric energy equiva¬ 
lent to nearly a million foot-pounds” had been trans¬ 
ported from Paris to Scotland in perfect safety. This 
statement was soon after confirmed by Sir William 
Thomson, to whom the box was consigned, and at the 
time attracted considerable attention. It was subse¬ 
quently ascertained that this box was really an im¬ 
proved secondary battery, constructed upon the plan of 
M. Camille Faure, who in 1880 conceived the idea of 
giving to the two plates of the cell to be constructed a 
preliminary coating of red lead, which rendered them 
much easier of reduction to the necessary condition for 
speedy charging. By M. Faure’s improvement the 
time spent in the formation of the cell was reduced 
from months to days. The ultimate result is the same 
as in the Plante cell—namely, the development, upon 
leaden plates immersed in acidulated water, of a coat- 


OTHER APPLICATIONS OF ELECTRICITY. 343 

ing of peroxide of lead, which may easily and quickly 
be reduced to the loosely crystalline metallic condition. 
By the process of “formation,” in which the current 
fiom a dynamo-electric machine is sent through the 
secondai y cells for several days without intermission, 
the coating of red lead is on one plate transformed 
gradually to a spongy metallic state, and on the other 
to a spongy surface of peroxide of lead. 

Since the improvement of M. Faure was made pub¬ 
lic many modifications of his process, as also innumer¬ 
able alternative methods of achieving the same result, 
have been introduced. It may be here stated that an 
important part of Faure’s process was the protection 
of the red-lead coating of the plates by means of en¬ 
velopes of flannel or felt ; and that the great majority 
of his successors present no other novelty than to dis¬ 
pense with these envelopes, and to substitute perfora¬ 
tions, channels, or grooves in the lead plates, by which 
the adhesion of the oxide is facilitated. 

It was thought by many, upon the introduction of the 
Faure cell, that the difficulties attending the storage of 
electrical energy had all been overcome, and that re¬ 
sults heretofore impossible were now to be gained; but 
it does not, after a lapse of two years, appear that these 
expectations have been realized, except to a very limited 
extent. 

297. Give a description of the Plante cell. 

A containing-vessel of any suitable material, such as 
glass or earthenware, is partly filled with a solution 
consisting of nine-tenths water and one-tentli sulphuric 
acid. In this liquid two sheets of lead rolled together, 
but kept from touching by strips of rubber rolled be¬ 
tween them, are placed. Figure 147 represents the 
appearance of the sheets while being rolled, and also 
shows them after they are rolled into form. 

An air-tight stopper, in which is a hole for introduc¬ 
ing or withdrawing the liquid and for the escape of gas, 
covers the vessel, which is very tall. The battery at 


344 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


this stage of its manufacture is represented by Figure 
148. The whole is now surmounted by an ebonite cover, 
which is fitted with two binding-screws to attach to the 



permanently connected with the leaden plates. This 
cell, as already indicated, is inert until one of the 

electrodes becomes completely oxi¬ 
dized, which, when the cell is new, 
takes a very long time. When, how¬ 
ever, the cell has once been brought 
to its proper condition it is recharged 
very quickly. The charging may be 
done by the use of two or three Grove 
or chromic-acid cells, as shown in 
the accompanying engraving, or by a 
dynamo-electric machine. 

The “ forming ” of the cell, after it 
is once set up, simply consists in 
alternately passing the charging cur¬ 
rent through it and discharging it, 
each alternate charge being sent 
through the secondary cell in the 
opposite direction to the one imme¬ 
diately preceding. The time of each charge is gradually 
increased, and the work of formation thus goes on for 























































































OTIIEH APPLICATIONS OF ELECTRICITY. 


345 


several months, until a thoroughly formed cell is pro¬ 
duced. The electro-motive force of this cell when fully 
charged may be as high as 2.38 volts ; and as its internal 
resistance is not greater than 0.12 of an ohm, the current 
through a short wire of large size is of very considerable 



strength. As a method of economically charging a 
number of these cells, M. Plante adopted the plan lepie- 
sented by Figure 150. The cells, arranged in a frame as 
shown, are surmounted by a rotatory commutator, or 
circuit-changer, which, when turned in one way, connects 
them in multiple arc, so that the entire series, irrespec¬ 
tive of number, may all be regarded as one cell; and 
which, when turned to a right angle from this position, 
connects them in series, the positive pole of the first to 




































































































346 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

the negative of the next, and so on. By this arrange¬ 
ment a great number of secondary cells can be simul¬ 
taneously charged in multiple by a couple of cells of 
acid battery, and may then be turned into a serial 
arrangement for use by simply rotating the commutator. 
This is very convenient when strong currents are re¬ 
quired for a short time, as for experimental or instruc¬ 
tive purposes, as it produces all the effect of a large 



Fig. 150. 


number of Grove cells without the trouble and expense 
of setting them up. 

298 . How may a small secondary battery be easily construct¬ 
ed illustrating the foregoing principles l 

Take a glass of any convenient size and shape (a tum¬ 
bler, for example), and nearly fill it with water acidu¬ 
lated with one-eighth of its bulk of sulphuric acid. 
Now cut two small strips of clean sheet-lead of a size to 
match the glass, perhaps three inches long, three-quar- 


























































































































































































OTHER APPLICATIONS OF ELECTRICITY. 347 

ters of an inch wide, and one-sixteentli of an incli thick. 
A card-board cover may be made for the glass, with two 
silts cut in it so that the ends of the lead strips may 
be passed through and bent over ; they are thus held in 
place, and the ends which pass through are fastened to 
wires. Couple up two or three cells of any battery (the 
gravity battery will do; in series, and one of the battery 
wires with one of the lead strips, and the other battery 
wire to the other strip. The lead strip attached to the 
wire leading from the positive pole of the battery will 
soon be seen to have a deposit of an o*xide of lead formed 
on it. After the action has continued for a short time, 
if the battery wires are disconnected and the wires at¬ 
tached to the leaden plates are connected together with 
a galvanometer in circuit, a current may be observed 
passing in the opposite direction to the original current. 

An ordinary gravity cell lias an electro-motive force 
of about one volt. It takes about three volts to form 
a secondary cell; and when formed and completely 
charged it has an electro-motive force of about two 
volts. 

299 . How is the secondary cell, as improved by Fanre, con¬ 
structed i 

The improvement of M. Faure consists chiefly in the 
adaptation and adop¬ 
tion of devices which aid 
materially in shortening 
the tedious process of 
formation. This is ac¬ 
complished by giving 
each of the leaden plates 
a thick coating of red lead prior to its immersion in the 
dilute acid. A box is provided with guides in the ends, 
and in these guides flat sheets of lead, heavily paint- 
ed with a paste made of red lead and dilute acid, are 
placed ; a piece of felt is pressed against each side, in 
order to retain the red lead in position. As indicated 
in the annexed diagram, the sheets of lead are arranged 



Fig. 151. 





















348 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 

like the plates of a condenser ; those attached to one 
end of the box being interleaved with those of the other 
end, but kept from touching them. All the sheets on 
one side are connected with a binding-screw, to which 
one of the leading-in wires is attached; and the sheets 
fixed to the other side are correspondingly connect¬ 
ed together, and also with a second binding-screw for 

the other lead¬ 
ing-in wire. The 
cell then pre¬ 
sents the appear¬ 
ance shown in 
Figure 152. The 
box is filled up 
with dilute acid, 
and a charging 
current is sent 
through it for 
over a week, 
when the red lead is reduced gradually on one side to 
metallic lead, and on the other is developed into the 
peroxide of lead. 

300 . What is meant by the popular expression “ storage of elec¬ 
tricity ” f 

The popular term is a misnomer, and rightly stated 
should be the “ electrical storage of energy.” 

The real state of the case is that by means of electri¬ 
city chemical work is done, and energy is thereby stored 
up; so that if Ave permit the chemical work to react 
electrical currents in a reverse direction are generated. 

In other words, the phrase “storage or accumulation 
of electricity ” means simply the combination, by means 
of electricity, of certain elements and compounds in a 
certain way, by which a tendency to react, and so pro¬ 
duce electrical currents, is given to the said combina¬ 
tion. 

301 . Have secondary batteries become commercially successful ? 

No ; these batteries have, up to the present time, not 







































OTHT.lt APPLICATIONS OF ELECTKICITY 


349 


been so successful or so useful as might have been ex¬ 
pected from the statements made in regard to them 
when the dame cell was first introduced ; and it is very 
clear that a commercially successful and practical sys¬ 
tem of storage of electrical energy has yet to be de¬ 
veloped. It is certain that a force which has once been 
evol\ ed and utilized to do work must be more costly 
Wxien leproduced than when first developed, by the 
cost of the work done; that is, even supposing there is 
no loss in the transformation, first, of electrical energy 
into chemical energy, and, secondly, of the chemical 
back again into electrical energy. 

In point of fact, however, a considerable loss occurs 
in storage. 

Several important considerations militate against the 
use of the secondary cell, made even in the best method 
now known. 

These are as follows: The first cost, which is very 
great; the expense and time required in charging; 
their great weight and bulk—each cell weighing at least 
fifty pounds—and the necessity of a great number of 
cells to work even a single incandescent lamp. To these 
must be added the comparatively high internal resist¬ 
ance of the Faure cell, as generally constructed, some of 
them showing a resistance as high as half an ohm. It 
must be stated, however, that it has valuable qualities 
—namely, portability, lessened risk from high-tension 
currents, steadiness in production within certain limits, 
and also the fact that, although it takes a great number 
of cells to work one lamp, the same number can, prop- 
perly arranged, operate several lamps. 

There can be no doubt that if these batteries are even¬ 
tually proved to be practical they will give a great im¬ 
petus to electric lighting. 

302 . Has electricity been applied to other purposes than those 
already described f 

Yes, the applications of electricity are too numerous 
to be mentioned here; many of the proposed applica- 


350 ELECTRICITY, MAGNETISM, AND TELEGRAPHY 

tions of the force, however, are impractical and vision¬ 
ary. 

It has been used as a means of measuring the velocity 
of rapidly moving bodies, such as cannon-balls, for per¬ 
forming upon musical instruments, for gas-ligliting, and 
even for killing whales. 

The only application which it is necessary to speak of 
here is that of gas-lighting. This lias been done in seve¬ 
ral ways. By using a thermo-electric battery, and Hash¬ 
ing a spark produced by the current between two pla¬ 
tinum contact-points placed directly over the burner. 
In this case the current first attracts an armature and 
opens a conical gas-stopper ; this plan is, therefore, well 
adapted for street-lighting. A second way is to ar¬ 
range the secondary circuit of an induction-coil with 
points over each burner, making the circuit in a num¬ 
ber of sections, so that one section can be lighted after 
another. This plan utilizes the secondary current. A 
third plan, much used in private houses and work¬ 
shops, is adapted for individual burners. Six or seven 
cells of a suitable battery are placed in circuit with a 
large, continuous coil of covered wire with a soft-iron 
core, and a circuit-closer also in the circuit is fixed 
upon each burner, so that the act of turning on the gas 
brings the two points of the circuit-closer into moment¬ 
ary contact with one another just over the escaping gas. 
The spark occurs at the moment when the points again 
separate, and is partly due to the extra current result¬ 
ing from the self-induction of the convolutions of the 
coil, and partly to the magneto-currents generated by 
the demagnetization of the core. 


CHAPTER XXIY. 

ODDS AND ENDS. 

The tenacity of a copper wire is diminished after an 
electric current lias for some time passed through it. 
In an iron wire the tenacity, in the same circumstances, 
increases. 

A piece of wood cut from a tree is a good conductor ; 
let it be heated and dried, it becomes an insulator ; let 
it be baked to charcoal, it becomes a good conductor 
again; burn it to ashes, and it becomes once more an 
insulator. 

Professor G. S. Ohm was born March 16, 1787; died 
July 7, 1854. 

Wheatstone’s bridge was devised by S. Hunter Chris¬ 
tie in 1833, and is described in the “Philosophical 
Transactions,” February 28, 1833. 

According to Faraday, so small a quantity of electri¬ 
city is stored in a Leyden jar that the decomposition of 
a single grain of water required 800,000 discharges of 
his large Leyden battery. 

Sir Charles Wheatstone was born in 1802; died Oc¬ 
tober 19, 1875, aged seventy-three. 

The incandescent electric light was first patented in 
England by an American named Starr, in the name of 
Edward Augustin King. The number of the patent is 
10,919, and the date November 4, 1845. 

A. Graham Bell’s first telephone patent was issued 
March 7, 1876, and is numbered 174,465. 

The second patent for the Bell telephone bears date 
January 30, 1877, and number 186,787. 

The resistance of the primary circuit of the induction- 

351 


352 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


coil of a Blake transmitter is from two-tenths to three- 
tenths of an ohm. 

The resistance of the secondary circuit averages about 
one hundred and fifty ohms. 

The resistance of a Bell teleplione-coil is about sev¬ 
en tv-live ohms. 

Speaking of duplex and other multiple telegraphs, 
Sabine’s “History and Progress of the Electric Tele¬ 
graph,' 1 republished in 1869, says: “Telegraphing in 
opposite directions, and telegraphing in the same di¬ 
rection, more than one message at a time, must be 
looked upon as little more than ‘feats of intellectual 
gymnastics,’ very beautiful in their way, but quite use¬ 
less in a practical point of view.” 

The discovery of the Leyden jar was first announced 
in a letter addressed on the 4tli of November, 1745, by 
Kleist, a Pomeranian ecclesiastic living in the town of 
Cammin, to Dr. Lieberkuhn, of Berlin. 

It was rediscovered the following year by Cuneus, a 
pupil of Professor Musclienbroek. 

Michael Faraday was born September 22, 1791, and 
died August 25, 1867. 

The first practical electro-magnet was made in 1825 
bv William Sturgeon. 

DuYernev, in 1700, Avas aware that the limbs of a frog 

%y 7 C? 

were convulsed by the action of electricity. 

TA\ T entv-two years before that date “ SAvammerdam 
showed the Grand Duke of Tuscany that Avlien a portion 
of muscle of a frog’s leg, hangingby a thread of nerve, 
bound Avith silver wire, was held over a copper support 
so that both nerve and wire touched the copper, the 
muscle immediately contracted.” Not until 1786 did 
Galvani make the same discovery, upon which Avas 
based the so-called science of galvanism, which was 
later ascertained to be one of the most useful develop¬ 
ments of electriciW. 

It has been demonstrated by experiment in England 
that one mile of buried or submerged cable develops as 


ODDS AND ENDS. 


353 


mucli electro-static capacity as twenty-three miles of 
ordinary overhead wire. 

Volta invented and described the electrophones in 
1776. 1 

The fiist magneto-electric machine was constructed in 
1833 by Pixii. 

The Siemens armature was invented in 1857 by E. 

ernei Siemens, and is now universally employed in 
the well-known magneto-telephone bell. 

Sulzer, of Berlin, in 1762, is believed to have been the 
first who noticed the peculiar taste occasioned by a 
piece of silver and a piece of lead when placed in con¬ 
tact with each other and with the tongue. 

This is the earliest suggestion of the voltaic battery. 

In 1800 Volta announced his invention of the battery. 

It is stated in the 1852 edition of the “Encyclopaedia 
Britannica” that in May, 1793, a voltaic pile was con¬ 
structed and used by a Mr. John Robison, the publi¬ 
cation of the account being made by Dr. Fowler, of 
Edinburgh. 

The current generated in a magneto-telephone is esti¬ 
mated by De la Rue not to exceed that which would 
be produced by one Daniell cell in a circuit of copper 
wire four millimetres in diameter, and of a length 
sufficient to go two hundred and ninety times round 
the earth. 

Oersted discovered in 1819 that a freely and horizon¬ 
tally suspended magnetic needle would deflect under the 
influence of an electric current. 

Romagnosi, of Trente, made and published the same 
discovery in 1805. 

The electric light was first produced by Sir Humphry 
Davy in 1802. 

Faraday discovered that electricity could be produced 
from magnets in 1831. 

The dynamo-electric machine is first described in a 
patent issued in England, October 14, 1854, to Soren 
Hjorth, and was reinvented in 1866 by four persons— 


354 ELECTRICITY, MAGNETISM, AND TELEGRAPHY. 


Alfred Varley, who also patented his machine, Werner 
Siemens, Sir Charles Wheatstone, and Moses G. Farmer. 

Galvanized iron wire, to have the same conductivity as 
the same length of copper wire, should weigh about six 
times as much per unit of length. 

The resistance tier mile of iron wire at sixty degrees 
Fahrenheit is ascertained in ohms by dividing 395,000 
by the square of the diameter of the wire in mils. 

A mil is one-thousandth of an inch. 

The resistance of iron wire increases about thirty-live 
hundredths per cent, for each additional degree. 

The resistance per mile of pure copper wire at sixty 
degrees Fahrenheit may be found by dividing 54,892 by 
the square of the diameter in mils. 

The resistance of copper wire increases about twenty- 
one liundreths per cent, for each additional degree 
Fahrenheit. 

Ampere, the founder of the science of electro-dy¬ 
namics, was born in January, 1775 ; died in June, 1836. 

The identity of lightning and electricity was discovered 
and demonstrated by Benjamin Franklin in 1747. 

The first lightning-rod was erected by Franklin upon 
his own house in 1752. 

Franklin, the father of American electricians, was 
born in Boston January 17, 1706, and died in Phila¬ 
delphia April 17, 1790. 

The first experimental gutta-percha insulated cable 
was made and submerged in September, 1847, at Bound 
Greek, between Newark and Elizabeth, New Jersey, by 
John J. Craven. A similar cable was laid by the Mag¬ 
netic Telegraph Company across the Passaic River in 
February, 1848, and across the Hudson River June 15, 
1848, the latter being one mile in length, all of which 
were successful. 

The first long submarine telegraph-cable was laid 
across the English Channel in August, 1850. 

A hen called upon to give his opinion concerning the 
nature of electricity, Faraday gave utterance to the fol- 


ODDS AND ENDS. 


355 


lowing remarkable statement : “ There was a time when 
I thought I knew something about the matter; but the 
longer I live, and the more carefully I study the subject, 
the more convinced I am of my total ignorance of the 
nature of electricity.” 

Philip Reis, the inventor of the now well-known Reis 
telephone, died January 14, 1874. 

In "W heatstone’s bridge systems, when the galvanome¬ 
ter resistance is greater than the battery resistance, the 
galvanometer should be made to connect the junction of 
the two greater resistances with that of the lesser. 

The dip of the magnetic needle was discovered in 
1576 by a compass-maker named Norman. 

M. Steinlieil, though not the first to use the earth as 
a portion of an electrical circuit, was the first to com¬ 
plete the circuit of a voltaic battery through the earth, 
and to use the earth circuit in telegraphy. 

Steinheil died September 14, 1870. 

S. F. B. Morse, the inventor of the electro-magnetic 
telegraph, was born April 27, 1791 ; died April 2, 1872. 

Professor Leonard D. Gale, in a deposition in con¬ 
nection with a telegraphic lawsuit in 1851, said: “ I 
saw Mr. Morse translate a message, while in an ad¬ 
joining room to the magnet, by the sound only. This 
was in the city of New York in 1837.” 

The first printing telegraph was invented by Alfred 
Yail in 1837. 

The conducting power of carbon is much lower than 
that of the metals, and instead of decreasing, as in the 
metals, with a rise in temperature, it decreases. 


356 ELECTRICITY, MAGNETISM, AND TELEGRAPHY 


INTERNATIONAL MORSE CHARACTERS. 


A__ 

A_ 

F_ 

H_ 

K_ 

N- 

R_ 

U_' 

U- 




ALPHABET. 

B_ 

D_ 

G_ 

I 

I_ 

0 _ 

S_ 

V_ 

X_ 

NUMERALS. 

2 - 

5 _ 

0 --- 


E - 

M_ 

P_ 

Q- 

T _ 

W__ 


3 _ 


PUNCTUATION MARKS. 


Period (.)_ Comma (,)____ 

Interrogation (?)_ Exclamation (!)__ 










ODDS AND ENDS 


357 


AMERICAN MORSE CHARACTERS. 


ALPHABET. 


A 

B- 

C- 

D__ 

E _ 

F_ 

G 

H_ 

1 — 

J- 

K_ 

L_ 

M_ 

N_ 

0 _ _ 

P 

Q- _ 

R __ 

s___ 

T _ 

U_ 

V_ 

W_ 

X 

Y_ 

z_ 

&— 


NUMERALS. 



PUNCTUATION MARKS. 

Period (.)_Comma (,)-— 

interrogation (?)_ Exclamation (!)-« 








TABLES. 


TABLE I. 

(From Culley's Hand-Book). 
COPPER WIRE. 


Birmingham 

Wire Gauge (Ap¬ 
proximate). 

Diameter. 

Number of 
yards in 1 
pound. 

Weight in pounds 

of 1 mile (1760 

yards). 

Resistance of 1 

mile of pure 

Copper at 32 0 

Approximate 

weight of Silk re¬ 

quired to cover a 
pound of Wire 

singly. 


Inches. 

Milli¬ 

metres. 




Oz. 

4/4 

.2302 

5- 8 47 

2.095 

84O.O9 

I.OO 



5 

.226 

5-740 

2-175 

809.20 

I.C38 



6 

.198 

5.029 

2.834 

62 I.OO 

I- 35 2 



7 

.183 

4-648 

3 - 3 i 7 

530-59 

i- 5 8 3 



8 

•175 

4-445 

3.628 

485.IO 

1-731 



9 

.160 

4.064 

3 - 35 ° 

404.60 

2.068 



IO 

.136 

3-454 

6.007 

292.99 

2.867 



11 

.128 

3 - 2 5 1 

6.781 

2 59-55 

3-237 



12 

.107 

2.717 

9-705 

l 8 l .35 

4.623 



13 

• IO 

2 -54 

11.11 

158.41 

5-300 



• • 

.092 

2 - 33 6 

13-125 

134-40 

6.266 




.08 

2.032 

1 7*36 

IOI.39 

8.288 




.07 

1.778 

22.67 

77-63 

10.82 



i6 

.065 

1.651 

26.29 

66.96 

12.25 



• • 

.0625 

1-587 

28.472 

6l.8l 

13-59 

> 


• • 

.06 

i- 5 21 

30.864 

57.02 

14-73 



i 7 

.058 

i -473 

33-°3 

53-29 

15-76 



• • 

.056 

1.422 

35-432 

49.67 

16.91 



• • 

•054 

i*37i 

38.104 

46.I9 

18.18 



• • 

.052 

1.32 

41.091 

42.83 

19.61 



18 

•°5 

1.274 

44.444 

39.60 

21.21 


72 

• • 

.048 

1.219 

48.225 

36.50 

23.02 



• • 

.046 

1.168 

52 - 5 i 

33-52 

25.06 



i 9 

.044 

1.117 

57-39 

30.67 

27-39 



• • 

.042 

1.066 

62.98 

27.94 

30.06 



20 

.04 

1.016 

69.444 

25-34 

33-14 



• • 

.038 

• 9 6 5 

77.16 

22.8l 

36.72 

\ 


21 

.036 

• 9 X 4 

85.766 

20.52 

40.92 



• • 

•034 

.864 

95- 2 9 

18.47 

45.48 


V\ 

• • 

.032 

.813 

108.5 

l6.22 

5 1 -79 



22 

•03 

.762 

123.46 

14.26 

5 8 -93 

> 



358 






























TABLES. 


359 


1 A B L E I.—( Continued ). 

copper wire. 



To find the percentage of conductivity in a sample of wire , pure copper 
being taken as = ioo : 

Divide the resistance of i mile of pure copper wire of the same size 
(column 6) by the actual resistance of i mile of the wire tested (re¬ 
duced to 32 0 Fahr.), and multiply by ioo. 












































360 


TABLES. 


TABLE II. 

DIAMETER, WEIGHT, RESISTANCE, AND BREAKING STRAIN OF 

IRON WIRE—E. B. B. 


{Prescott.) 


B.W. Gauge 
No. 

Diameter in 
thousandths 
of inch. 

Resistance at 

76° Fahrenheit. 

Weight in pounds 
per mile. 

Breaking strain 
in pounds. 

Feet 

per ohm. 

Ohms 
per mile. 

I 

3 °° 

i 35 ° 

3 9 i 

1249 7 

4000 

2 

284 

1211 

4 - 3 6 

1120.0 

3400 

3 

2 59 

1008 

5 ,2 4 

93 r -5 

29OO 

4 

238 

958 

5 - 5 i 

8S6.6 

2500 

5 

220 

727 

7.26 

673.0 

2 200 

6 

203 

618 

8-54 

572.0 

1S00 

7 

180 

578 

10.86 

449-9 

1520 

8 

i6 5 

409 

12.92 

378.1 

1200 

9 

148 

328 

16.10 

304.2 

950 

IO 

i 34 

269 

19.60 

249.4 

820 

11 

120 

216 

24.42 

200.0 

650 

I 2 

109 

i 79 

29.60 

165.0 

5 IQ 

13 

95 

i 35 

39.00 

I2 5-3 

400 

14 

83 

104 

5 1 - 00 

95 7 

35 ° 

15 

72 

78 

67.83 

72.0 

3 °° 

16 

6 5 

6 3 

83.20 

58.7 

200 

17 

58 

55 

96 00 

5°-9 

I 5 ° 

l8 

49 

35-9 

147.00 

33-3 

1 *5 

19 

42 

26.0 

* 99-34 

24*5 

85 

20 

35 

18.4 

287.30 

17 0 

65 



















TABLES 


361 


TABLE III. 


SHOWING THE DIFFERENCE BETWEEN WIRE GAUGES. 


No. 

London. 

Stubs. 

Brown & 
Sharpe’s. 

No. 

London. 

Stubs. 

Brown & 
Sharpe’s. 

OOOO 

•454 

•454 

.460 

19 

.040 

.042 

•03589 

OOO 

.425 

.425 

.40964 

20 

•035 

•035 

.03196 

OO 

.380 

.380 

.36480 

21 

•0315 

•032 

.02846 

o 

•340 

• 340 

•32495 

22 

.0295 

.028 

•025347 

I 

.300 

.300 

.18930 

23 

.027 

.025 

.022571 

2 

.284 

.284 

•25763 

24 

.025 

.022 

.0201 

3 

.259 

.259 

.22942 

25 

.023 

.020 

.0179 

4 

.238 

.238 

.20431 

26 

.0205 

.018 

•01594 

5 

.220 

.220 

.1S194 

27 

.01875 

.016 

.OI4I95 

6 

.203 

.203 

.16202 

28 

.0165 

.OI4 

.OI264I 

7 

. 180 

.180 

.14428 

29 

.0155 

.013 

.OII257 

8 

.165 

• 165 

. 12849 

30 

•01375 

.012 

.010025 

9 

. 148 

. 148 

•I 1443 

31 

.01225 

.OIO 

.008928 

IO 

.134 

•134 

.IO189 

32 

.01125 

.009 

00795 

11 

. 120 

. 120 

.O9O74 

33 

.01025 

.00S 

.00708 

12 

. 109 

. 109 

.08081 

34 

.OO95 

.007 

.0063 

13 

.095 

•095 

.07196 

35 

.009 

.005 

.OO561 

14 

.083 

.083 

.06408 

36 

•OO75 

.004 

.005 

15 

.072 

.072 

.05706 

37 

.0065 

• • • • 

•OO445 

16 

.065 

.065 

.05082 

3 S 

•OO575 

• • • • 

.OO3965 

17 

.058 

.058 

.04525 

39 

.005 

• • • • 

•OO353I 

18 

.049 

.049 

.04030 

40 

.OO45 

- • • • 

.OO3144 


TABLE IV. 


APPROXIMATE WEIGHT OF INSULATED WIRES—AMERICAN 

GAUGE. 

Braided Wire. 


No. 

<( 

A . 

. 8 

ft. 

to lb. 

*T * * * *. 

6 . 


ft 

tt 

<< 

« . 


it 

tt 

a 

T 9 . 


U 

tt 

tt 

T 9 . 


tt 

tt 

tt 

T 4 , .. 


tt 

tt 

tt 

A .. 

l6.. **.....*•*« 


tt 

tt 

if 

17 . 

. 120 

tt 

tt 

tt 

.. 

t 8 . 


it 

U 

tt 



tt 

tt 

tt 

...*. 


u 

tt 








































362 


TABLES. 


TABLE IV.—( Continued '). 

APPROXIMATE WEIGHT OF INSULATED WIRES—AMERICAN 

GAUGE. 

Double-Wound Wire. 



Owing to the difference in gauges, and to the fact that nearly every 
manufacturer has his own gauge, it is almost impossible to compile a 
standard table of the properties of iron wire with anything more than ap¬ 
proximate exactness. Hence the figures in Table 2, which is taken from 
Mr. Prescott’s book, is more a table of what the wire should be than what 
it is. The short table we give below will be found to be nearer the mark 
for the gauges to which it refers. 


TABLE V. 

STANDARD WEIGHT AND RESISTANCE OF GALVANIZED WIRE. 



No. 

Resistance. 

■ 

Weight. 

Per mile. 

6 

IO 

ohms. 

538 lbs. 

t i 

7 

12.1 

U 

461 

u 

i i 

8 

I4.I 

a 

389 

u 

i i 

9 

16.4 

it 

3 2 3 

a 


10 

20. 

a 

264 

u 

a 

11 

2 5- 

<< 

211 

« 

u 

12 

3 2 -7 

a 

163 

a 

(i 

14 

52.8 

a 

97 

u 

i c 

16 

91.6 

u 

57 

a 




















TABLES. 


363 


TABLE VI. 

RESISTANCE AND WEIGHT TABLE FOR COTTON AND SILK COVERED 
AND BARE COPPER WIRE—AMERICAN GAUGE. 

The resistances are calculated for pure copper wire. Our 
wire is about 98 per cent, of the conductivity of pure copper. 

The number of feet to the pound is only approximate for 
insulated wire. 



Feet per pound. 


Resistance, Naked Copper. 

No. 

Cotton 

Covered. 

Silk 

Covered. 

Naked. 

Ohms per 
1000 feet. 

Ohms 
per mile. 

F eet 
per ohm. 

Ohms 
per pound. 

8 

• • • • 

• • • • 

20 

.6259 

3-3 

1600. 

.0125 

9 

• • • • 

• • • • 

2 5 

.7892 

4.1 

1272. 

.OI97 

10 

• • • • 

• • • • 

3 2 

.8441 

4.4 

U85. 

.0270 

11 

• • • • 

• • • • 

40 

I.254 

6.4 

798 . 

.0501 

12 

42 

46 

5 ° 

1.58° 

8-3 

633 * 

.079 

T 3 

55 

60 

64 

i *995 

10.4 

504 . 

.127 

14 

68 

75 

80 

2.504 

13.2 

400. 

.200 

i 5 

87 

95 

101 

3.172 

16.7 

316. 

.320 

16 

110 

120 

128 

4.001 

2 3 * 

230. 

•5 12 

17 

140 

I 5 ° 

161 

5-°4 

26. 

I98. 

.811 

18 

175 

190 

203 

6.36 

33 * 

i 57 * 

1.29 

*9 

220 

240 

256 

8.25 

43 - 

121. 

2.11 

20 

280 

305 

3 2 4 

10.12 

53 * 

99. 

3 -27 

21 

36° 

39 ° 

408 

12.76 

68. 

76.5 

5.20 

22 

45 ° 

490 

5*4 

16.25 

85 * 

61.8 

8-35 

23 

560 

6l 5 

649 

20.30 

108. 

48.9 

x 3-3 

24 

7 J 5 

775 

818 

25.60 

i 35 * 

39 -° 

20.9 

2 5 

910 

990 

1030 

32.2 

170. 

31.0 

33-2 

26 

1165 

1265 

1300 

40.7 

214. 

24.6 

52.9 

27 

1445 

1570 

1640 

51*3 

270. 

i 9-5 

84.2 

28 

1810 

1970 

2070 

64.8 

343 * 

i 5-4 

i 34 . 

29 

2280 

2480 

2617 

81.6 

43 2 - 

12.2 

213. 

3 ° 

2805 

3 ° 5 ° 

3287 

103. 

53 8 - 

9.8 

338 . 

3 1 

3 6o 5 

392° 

4 r 44 

130. 

685. 

7-7 

539 - 

3 2 

4535 

4930 

5 22 7 

164. 

865. 

6.1 

856. 

33 

34 

• • • • 

6200 

6590 

206. 

1033 * 

4.9 

1357 * 

• • • • 

7830 

833° 

260. 

1389. 

3-8 

2166. 

35 

• • • • 

983° 

10460 

328. 

18 20. 

2.9 

3521 * 

5469* 

3 6 

• • • • 

12420 

13210 

414. 

2200. 

2.4 













































364 


TABLES. 


TABLE VII. 

SHOWING THE RELATIVE CONDUCTIVITY AND RESISTANCE OF 

METALS. 


Pure Metals. 

Conductivity — Silver 
at 32 0 being 100. 

Resistance—Silver 
at 32° taken as 1. 

Aluminum. . 

33-76 

2.96 

Antimony. 

4.62 

21.65 

Arsenic. 

4.76 

2 I.OI 

Bismuth. 

12 5 

80.OO 

Cadmium. 

23.72 

4.21 

Cobalt. 

17.22 

58.07 

Copper (hard). 

99-95 

1.00 

(soft). 

97-95 

• • • • 

Gold . 

77.96 

1.28 

Iron. - , . 

16.81 

5-95 

Lead . 

8.32 

12.02 

Mercury . 

1.63 

6i.35 

Nickel . 

13.m 

7-63 

Platinum . 

ro 

O 

00 
1—1 

5-55 

Silver (hard). 

IOO. 

1. 

“ (soft) . 

I08.57 

0.92 

Thallium . 

9.16 

10.92 

Tin . 

I2.36 

8.09 

Zinc (pressed) . 

29.O2 

3-44 

Graphite . 

O.69 

145.00 


TABLE VIII. 

SHOWING THE RELATIVE RESISTANCES OF LIQUIDS. 


(Becqiterel.) 


Copper taken as standard. 

Solution sulphate of copper, saturated. 

“ “ “ diluted to half 

“ “ of zinc, saturated. 

diluted to half.. 

Chloride of sodium ) . , 

/ V saturated. 

(common salt) \ 

Chloride of sodium, diluted to half. 

Sulphuric acid, diluted i to n. 

Nitric acid. 

Distilled water.. 


16,855,520 

26,327,637 

15,861,267 

12,835,836 

2 , 903^38 

3<9 6 5>42i 

1,032,020 

976,000 

6,754,208,000 











































TABLES. 


365 


TABLE OF RELATIVE CONDUCTIVITIES. 


Silver, 

Saline Solutions, 

Glass, 

Copper, 

Rarefied Air, 

Sealing Wax, 

Gold, 

Melting Ice, 

Sulphur, 

Zinc, 

Platinum, 

Distilled Water, 

Resin, 

Stone, 

Gutta-Percha, 

Iron, 

Dry Ice, 

India-Rubber, 

Tin, 

Dry Wood, 

Shellac, 

Lead, 

Porcelain, 

Paraffine, 

Mercury, 

Dry Paper, 

Ebonite, 

Carbon, 

Wool, 

Dry Air. 

Acids, 

Silk, 


There is no known absolute conductor. In the foregoing table each 
substance conducts better than the one which follows it. 


ELECTRO-MOTIVE FORCE OF BATTERIES IN 


VOLT'S. 

-n -n Volts - 

Darnell. 1.079 

Grove. 1.956 

Smee, when not in action. 1.102 

when in action. 510 

Bunsen. 1.926 

Bichromate or Chromic Acid. 1967 

Marie Davy. 1.533 

Leclanche. 1.662 

Plante secondary. 2.100 

Faure “ . 2.100 


RELATIVE INDUCTIVE CAPACITIES OF THE PRIN¬ 
CIPAL INSULATING SUBSTANCES. 


Standard being air, taken as. 100 

Resin is 177 

Pitch “ 180 

Beeswax “ 186 

Grass “ 190 

Sulphur “ 193 

Shellac “ 195 

Paraffine “ 198 

India-rubber “ 280 

Gutta-percha “ . 4 2 ° 

Mica “ 5 °° 


The above are from Jenkin’s “ Electricity and Magnetism.” 























366 


TABLES. 


(From Gulley's Hand-book .) 
METRIC WEIGHTS AND MEASURES. 


Millimetres. 

Inches. 

Millimetres. 

Inches. 

Millimetres. 

Inches. 

I 

O.O39 

45 

I. 77 I 

125 

4.941 

2 

O.O78 

5 ° 

I.968 

130 

5 - 118 

3 

0.118 

55 

2.165 

135 

5-315 

4 

0-157 

60 

2.362 

140 

5 - 5 12 

5 

O.I97 

65 

2-559 

145 

5 - 7 o 8 

6 

O.236 

70 

2.756 

150 

5.906 

7 

O.275 

75 

2-953 

155 

6.103 

8 

0.315 

80 

3- I 49 

l 6 o 

6.299 

9 

o -354 

35 

3-346 

165 

6.496 

10 

0-394 

90 

3-543 

170 

6.693 

r S 

0.590 

95 

3-740 

I 75 

6.890 

20 

0.787 

100 

3-937 

180 

7-087 

2 5 

0.984 

io 5 

4-134 

185 

7.284 

30 

1.181 

110 

4 - 33 1 

190 

7.480 

35 

*•378 

115 

4.528 

i 95 

7.677 

40 

J -575 

120 

4-744 

200 

7-874 


i inch = 25.4 millimetres. 



Inches. 

Feet. 

Yards. 

1 Millimetre .... 

1 Centimetre... . 

1 Decimetre .... 

1 Metre. 

O.O39 

o -393 

3-937 

39-370 

39,370.790 

• • • • 

• • • • 

• • • • 

3.280 

3,280.899 

• • • • 

• • • • 

• • • • 

I.O93 

TO93.633 

1 Kilometre. 


Miles. 

1 

2 

3 

4 

5 

6 

7 

8 

9 

Kilometres 

1.609 

3.219 

4.828 

6-437 

8.047 

9656 

11.265 

12.874 

14.484 

_ 















































TABLES. 


367 


i 

i 

i 

i 

1 

2 

3 

4 

5 

6 

7 

8 


Milligramme. 

Centigramme 

Decigramme. 

Gramme 

Kilogramme. 

Kilogrammes 

u 

u 

u 

u 

u 

u 

u 


Grains Troy. 

Pounds Avoirdupois. 

O.OI5 

• • • • 

0-154 

• • • • 

1-543 

• • • • 

I 5 - 43 2 

• • • • 

I 5 G 3 2 - 34 S 

2.2046 

• • • • 

4.4092 

• t • • 

6.6138 


8.8184 


I I.O23O 


13.2276 


15.4322 


17.6368 


I9.8414 


7,000 grains Troy = i pound Avoirdupois, 
i Litre = 35.275 fluid ounces = 1.764 pints = 61.024 cubic 

inches. 

1 cubic centimetre = .0610 cubic inches. 


1 




























INDEX 


Aerial cables, 181 ; description of, 
182. 

Alarms, electric, operated by clock¬ 
work, 328. 

Alphabet, Morse telegraphic, 35G, 
357. 

Amalgamation of zincs, 25. 

Amber, 9. 

Ampere, 95. 

Applications (miscellaneous) of— 
Blasting, 329, 332. 

Clock-alarms, 828. 

Electric bells, 28G, 298. 

Electric clocks, 323, 327. 
Electricity, 2GG. 

Electric lighting, 2G6, 280. 
Electric-metallurgy, 281, 285. 
Electro-motion and transmission 
of power, 332, 340. 
Electro-therapeutics, 318, 322. 
Gas-lighting, 350. 

Storage of electric energy, 340, 349. 
Telephony, 299, 317. 

Time-balls and guns, 328. 
Armature, 48. 

Siemens, 67, 353. 

Arrangement of batteries for maxi¬ 
mum effect with given number, 
148, 150. 

Artificial magnet, 44. 

Astatic galvanometer, 100. 
Attraction of magnets, 44. 
Automatic circuit-breaker, 83. 

Bar magnet, 48. 

Batteries, electric, 18. 

Best arrangement for given num¬ 
ber of cells, 148, 150. 

Bunsen, 26. 


Batteries— 

Cal laud, 26. 

Care of batteries, 32, 84. 

Chromic acid, 26. 

Daniel 1, 26. 

Depolarizing mixture batteries, 26. 
Earth, 42. 

Gravity, 26. 

Grove, 26, 28. 

Internal resistance of, 118, 121 
Invention of, 353. 

Leclanche, 26, 30. 

Local action in, 2o. 

Other methods of arranging, 145. 
Poles of, 31. 

Proportion merit to short lines, 148. 
Buie for obtaining greatest mag¬ 
netic effect from, 146. 
Secondary, 340. 

Single-fluid, 26. 

Smee, 26. 

Thermo-electric, 37. 

Two-fluid, 26. 

Usual arrangement of, for tele¬ 
graph lines, 136, 144. 

Voltaic, 24. 

Watson, 26. 

Bells, electric ^see electric bells, 286). 
Blasting by electricity, 329. 
Frictional, 380. 

Relative advantages, 332. 

Voltaic, 331. 

Brush dynamo, 74, 76. 

Cables, aerial, 181. 

Description of principal forms, 
182. 

Submarine, 189, 191, 354. 

Candle, electric, 277. 279. 


369 





370 


INDEX. 


Carbon battery, 29. 

Circuits, voltaic, 142, 152. 
Arrangement of, to connect regis¬ 
ter or sounder, 217. 

'Conditions of current strength in, 
144. 

Constitution of, 142. 

Earth as part of, 142, 144. 

Faults, 231, 233. 

Testing, 233, 241. 

Circuit-breaker, 83. 

Automatic, 83. 

Circuit-changers, 200. 

Circuit-closers, press-button, 291. 
Pull, 292. 

Clocks, electric, 323. 

Bain’s clocks, 323, 32G. 

Description of, 324. 

Governed clocks, Jones system, 32G. 
Shepherd system, 327. 
Closed-circuit system of telegraphy, 
133, 135. 

Coercive force of magnets, 48. 
Compound magnets, 48. 

Condensers, 85, 86. 

Coulomb, 95. 

Cross-arms, 155. 

Crosses, in telegraph or telephone 
lines, 232. 

Swinging, 233. 

To test for, 239. 

Weather, 233, 240. 

Current strength, 92, 93. 

Conditions of, in a circuit, 144. 
How varied, 93. 

Cut-outs, 203. 

Daniell battery, 26, 28. 

Care of, 32. 

Deflection, to compensate shunted, 
128. 

Dia-magnetism, 50. 

Dielectrics, 18. 

Differential galvanometer, 105. 

Dip of magnetic needle, 46. 
Disconnection, or break, in electric 
circuits, 231. 


Disconnection in district systems, 
235. 

Intermittent, 235. 

Partial, 236. 

To test for, 233. 

District telegraphs, 137. 

Duplex telegraphy, 242. 

Bridge, 247. 

Differential, 245. 

Gintl’s, 243. 

Historical sketch of, 243. 

Sabine’s opinion of, 352. 

Stearns’s, 244, 249. 

Duplicate transmission in same di¬ 
rection, 249. 

Du Yernay’s anticipation of Galva- 
ni’s discovery, 352. „ 

Dynamic induction, 19. 
Dynamo-electric machines, 69, 79. 
Arrangement to act as motors, 
336. 

Brush, 74, 76. 

Gramme, 72, 74. 

Invention of, 353. 

Reversibility of, 335. 
Ring-armature machines, 72, 76. 
Term defined, 76. 

Uses of, 79. 

Earth batterv, 42. 

Earth circuit, 142, 144. 

Early examples of, 143. 

First utilization in telegraphy, 142. 
Earth currents, 41. 

Method of obviating effects of, 41. 
Earth faults, 231. 

Intermittent, to test for, 239. 
Swinging, 232. 

To test for, 237. 

Earth wires, in offices, 193, 228. 
Defective, 233, 240. 

For lightning-arresters, 195. 

For testing purposes, 195. 

Proper construction of, 194. 

Uses of, 193. 

Electrical machines, 12. 

Cylinder machine, 14. 



INDEX. 


371 


Electrical Machines— 

Holtz machine, 16. 

Plate machine, 13. 

Electrical measurement, 98, 129. 
Electrical resistance, 91. 

Of wires, 91, 92. 

Electrical units, 93, 97. 

Electric battery, 18. 

Electric bells, 286. 

Arrangements lor various bell cir¬ 
cuits, 292, 296. 

Construction of simple bell circuit 
290. 

For telephone lines, 297. 
Individual, 297. 

Magneto, 297. 

Polarized, 2S8. 

Press-buttons for, 291. 

Pull circuit-closer, 292. 
Single-stroke. 287. 

Vibrating, 287. 

Electric clocks (tee clocks, electric, 
323). 

Electric gas-lighting, 350. 

Electricity a form of energy, 9. 
Atmospheric, 20. 

Battery, 18. 

Conductors of, 11. 

Distribution of, 18. 

Dynamical, 17. 

Electrical machines, 12, 16. 
Electrics and non-electrics, 12. 
Electrometer, 12. 

Electrophorus, 14. 

Electroscope, 12. 

Frictional, 10, 20. 

Magneto, 20, 59. 

Methods of developing, 20. 
Miscellaneous applications of, 266. 
Non-conductors of, 11. 

Oersted’s discovery, 353. 

Plus and minus, 11. 

Positive and negative, 10. 
Relationship to magnetism, 50, 51. 
Romagnosi’s anticipation of, 353. 
Statical, 17. 

Thermo, 20. 


Electricity— 

Vitreous and resinous, 10. 

^ oltaic or galvanic, 22. 

Electric lighting, 266. 

Arc, 266. 

Arc lamps, 268. 

Brush lamp, 269. 

Divisions of, 266. 

Edison’s lamp, 275. 

Electric candle, 277. 

First produced, 353. 

Illuminating power of, 277. 
Incandescent, 273. 

Jablochkoff candle, 277. 

Lane-Fox lamp, 276. 

Maxim, Bernstein, and Weston 
lamps, 277. 

Semi-incandescent lamps, 279. 
Starr’s lamp, 274. 

Sun lamp, 280. 

Swan’s lamp, 276. 

Wilde’s candle, 278. 

Electric potential, 89, 90. 

Electric quantity, 92. 

Term applied to current electri¬ 
city, 92. 

Applied to static electricity, 92 
Electrics and non-electrics, 12. 
Electrodes, 32. 

Electro-dynamic induction, 19. 
Electrolysis, 32. 

Electrolytes, 32. 

Electro-magnet, 19, 52. 

Construction of, 52. 

For long circuits, 56. 

For short circuits, 56. 

Length of core, 54. 

Resistance of, 54. 

When devised, 53, 352. 
Electro-magnetic induction, 19. 
Electro-magnetism, 52. 

Laws of, 54, 55. 
Electro-metallurgy, 281. 
Electro-plating, 281, 283. 
Electro-typing, 283. 

General explanation of, 281. 
Outline of art, 283. 








372 


INDEX. 


Electrometer, the, 12. 
Electro-motion, and transmission of 
power, 332 

Dynamo-machine as a motor, 

336. 

Froment’s motor, 333. 

Jacobi’s motor, 332. 

Page’s motor, 333. 

Power electrically transmitted, 

337, 340. 

Railways, 337, 338. 

Reversibility of dynamo-machine, 
335. 

Electro-motive force, 90. 

Comparison of, 124. 

Measurement of, 125, 126. 

Of batteries, 90, 91. 

Electrophorus, 14, 353. 

Electroscope, 12. 

Electro-static induction, 18. 
Electro-therapeutics, 318. 

Definitions of, 319. 

Electrical probe, 321. 
Electro-physiology, definition of, 
318. 

Electro-surgery, 320. 

Energy, definition of, 9. 

Escape in telegraph or telephone 
lines, 232. 

To test for, 238. 

Extra current, 84, 85. 

Farad, 96. 

Fire-alarm telegraphs, 136. 
Frictional electricity, 10. 
Applications of, 20. 

Galvanometer, the, 98. 

Astatic, 100. 

Constant of, 113. 

Definition of, 98. 

Differential, 105, 107. 

Invented by Schweigger, 99. 
Resistance, measurement of, 121, 
123. 

Sine, 104. 

Tangent. 101, 104. 


Galvanometer— 

Thomson’s reflecting, 107, 110. 

To reduce deflection of, 123. 

Uses of, 100. 

Wheatstone’s bridge, 110, 113. 
Gas-lighting, electric, 350. 

Gauge, wire, 166, 168. 

Gramme machine, 72, 74. 

Gravity batteries, 26. 

Care of, 33. 

Reactions of, 28. 

Ground wires, 193, 196, 228. 

For lightning-arresters, 195. 

For testing purposes, 195. 

Should be soldered, 195. 

To construct, 194. 

Uses of, 193. 

When to be used, 228. 

Grounds in telegraph or telephone 
lines, 231. 

Intermittent, 239. 

Swinging, 232. 

To test for, 237. 

Grove battery, 26. 28. 

Care of, 33. 

Harmonic telegraph, 254. 

Gray’s, 255. 

Holtz’s electrical machine, 16. 

Reversibility of, 16. 

Horseshoe magnets, 48. 

Illuminating power of the electric 
light, 277. 

Individual signals, 297. 

Induction, 18. 

Dynamic, or voltaic, 19. 
Electro-magnetic, 19. 
Electro-static, 18 
Magnetic. 20, 45, 46. 
Magneto-electric, 19, 59. 
Induction-coil, 80 
Circuit breaker, 83. 

Condenser, use of, 85. 

Description of large coils, 87. 
Primary circuit of, 82. 

Secondary coil of, 82. 



INDEX. 


373 


Induction-coil— 

Soft-iron core, 86. 

Use of in telephone transmitters, 
309. 

Uses of, 88. 

What it is, 80. 

Why so called, 80. 

Insulators for land lines, 159. 
Brooks’s, 164. 

Earthenware, 163. 

Glass, 163. 

Requisite qualifications of, 162. 
Rubber hook, 165. 

Joint resistance, 150. 

Calculation of, 151. 

Joints or splices in line-wire, 177. 
Bell-hanger’s joint, 178. 

Britannia joint, 178. 

Soldering, 178. 

Twist joint, 178. 

Kerite, what it is, 184. 

Keys, telegraph, 211. 

Care of, 226. 

Defects in operation, 225. 

Morse, 211. 

Open-circuit, 213. 

Reversing, 213. 

Ladd’s dynamo-electric machine, 70, 
72. 

Lamps, arc, 268, 273. 

Incandescent, 273, 277. 
Semi-incandescent, 279. 

Sun, 280. 

Leakage-conductors for land lines, 
160. 

Leclanche battery, 26, 30. 

Care of, 34. 

Leyden jar, 17. 

When discovered, 17, 352. 

Light, electric, 266, 280. 
Lightning-arrester, 201, 203. 
Liglitning-rod, 20. 

Line construction, 153. 

Conductors, material of, 165. 


Line— 

Cross-arms for, 155. 

Dip of, 175. 

Insulators, 159, 162, 165. 

Joints or splices, 177, 179. 

Poles for use in, 153, 155. 

Sizes of, 166, 169. 

To ascertain proper dip, 176. 
Lines, house-top, 155. 

Supports for, 156, 159. 

Lines, supplying a number from one 
battery, 146. 

Line-wire, 165, 175. 

Aerial cables, 181. 

For telephone lines, 169, 170. 
Galvanized, 170. 

Humming in, 179. 

Iron, 165. 

Method of leading into terminal 
station, 181. 

Method of leading into way-sta¬ 
tion, 179. 

Sizes chiefly used, 152. 

Steel, 169. 

Liquids, resistances of, 118. 

Magnet, 43. 

Artificial, 44. 

Natural, 43. 

Magnet, properties of, 44, 46. 

Bar, 48. 

Compound, 48. 

Dip, 46. 

Horseshoe, 48. 

Permanent, 47. 

Polarity, 46. 

Magnetic field, 49. 

Magnetic induction, 20, 45, 46. 
Magnetism, 43. 

Relationship to electricity, 50. 
Residual, 53. 

Rule for obtaining maximum ef¬ 
fect from given battery, 146. 
Magnetization, process of, 49. 
Magneto-bells, 297. 

Magneto-electric induction, 19, 59. 
Discovery of, 353. 




374 


INDEX. 


Magneto electricity, 20, 59. 
Advantages of, 62. 

Applications of, 61, 63. 
Magneto-electric machines, 60, 65. 
.Definitions of, 60, 65. 

First invented, 60. 

Mutual accumulation machines, 
69, 70. 

Wilde’s, 68, 69. 

Measurement of resistance, 115, 123. 
By differential galvanometer, 116. 
By substitution, 116. 

Internal resistance of batteries, 
119, 121,. 

Land lines, dispensing with earth- 
wires, 117. 

Resistance of galvanometer, 121, 
123. 

Using Wheatstone bridge, 116, 
117. 

Miscellaneous applications of elec¬ 
tricity, 266. 

Electric bells, 286. 

Electric lighting, 266. 
Electro-metallurgy, 281. 

Morse’s telegraph, 133, 136. 
Alphabet, 356, 357. 

Instruments, 196. 

Key, 211. 

Register, 215. 

Relay, 206, 209. 

Repeaters, 218, 221. 

Sounder, 214. 

Multiple telegraphy, 242. 

Duplex, 242, 250. 
Electro-harmonic, 254, 265. 
Quadruplex, 250, 254. 

Multiplying power of shunts, 128. 

Odds and ends, 351, 355. 

Office-wire, 192. 

Practical arrangement of, 192. 
Ohm, 94. 

Ohm’s law, 96. 

Application of, 97. 

Partial disconnection, 231. 


Partial disconnection, to test for, 
236. 

Permanent magnet, 47. 

Plates of battery, 31. 

Polarity of magnets, 46, 47. 
Polarization, voltaic, 23. 

Explanation of, 23. 

Injurious effects of, 24. 

Methods of obviating, 24. 

Polarized bells, 288. 

Polarized relay, 209, 211. 

Poles of battery, 31. 

Poles, for telegraph lines, 153. 

Setting up of, 154. 

Police telegraph, 139. 

Potential, definition of, 89, 

A relative term, 89, 90. 

Difference of, 90. 

Properties of magnets, 44, 46. 
Proportionment of battery power 
for short lines, 148. 

Quadruplex telegraphy, 250, 254. 
Changes and improvements in, 
253. 

Edison’s, 251. 

Historical sketch of, 250. 

Quantity, 92. 

Definition of, 92. 

Railways, electric, 337. 

Register, telegraphic, 215. 
Adjustments, and management 
of, 226. 

Relay, telegraphic, 206. 

Adjustments, 208, 222, 225. 
Construction, 206. 

Polarized, 209, 211. 

Use of, 206. 

Repeaters, telegraphic, 218, 221. 
Bulkley’s, 218. 

Button, 218. 

Edison’s, 221. 

Uses of, 218. 

Repulsion of magnets, 45. 

Residual magnetism, 45. 

Resistance, 91. 




INDEX. 


375 


Resistance— 

Internal of battery, 118. 
Measurement of, 119, 121. 

Of any given wire, 91, 92. 

Of a telegraph line, 91. 

Of battery in reference to entire 
circuit, 53. 

Of cells in common use, 119. 

Of electro-magnets, 54. 

Of human body, 321. 

Of liquids, 118. 

Resistance-coils, 114. 

Resistance, joint, 150. 

Calculation of, 151. 

Resistances, measurement of, 115, 
123. 

By differential galvanometer, 116. 
By substitution, 116. 

By tangent galvanometer, 120. 

By Wheatstone’s bridge, 116, 117. 
Retardation, 188. 

Rheostat, and resistance-coils, 113, 
115. 

Present arrangement, 114. 
Wheatstone’s, 113. 

Robison’s anticipation of Volta’s in¬ 
vention of the “voltaic pile,” 335. 
Ronald’s underground line, 184. 

Secondary batteries, 340. 

Faure cell, 347. 

Historical sketch of, 341. 

Plante cell, 343, 346. 

Small-size Plante, 346. 

Shunts, 126, 129. 

Compensation of shunted deflec¬ 
tions, 128. 

Definition of term, 126. 

Their use, 126. 

To ascertain multiplying power of, 

128. 

Value of shunts, 127. 

Siemens armature, 67. 

Signals for telephone lines, 297. 

Sine galvanometer, 104. 

Single-fluid battery, 26. 
Single-stroke electric bells, 287. 


Soldering joints in line-wire, 178. 
Sounder, 214. 

Adjustments of, 226. 

Spring-jacks, 205. 

Static, and dynamic, definition of, 16. 
Static induction, 18. 

Storage of electric energy, 340, 348, 
349. 

Submarine cables, 189. 

Adaptation for telephony, 190. 
Insulating material employed in, 
189. 

Subterranean lines, 184. 

Adaptation for telephonic circuits, 

185. 

Conductor usually employed, 184. 
First laid, 184. 

Static induction in, 185. 

Where now used, 185. 

Sulzer’s experiment in voltaic elec¬ 
tricity, 353. 

Swammerdam’s anticipation of Gal¬ 
van i’s discovery, 352. 
Switchboard, 197. 

Universal, 197. 

Uses of, 197. 

Western Union pin, 198. 

Switches, and circuit-changers, 200. 
Automatic telephone, 200, 315,317. 
Button, 200. 

Cut-out, 203. 

For changing circuit between 
sounder and register, 217. 

Plug, 200. 

Secrecy, 200. 

Tables, of copper wire, 358, 359. 
Difference between wire-gauges, 
361. 

Electro-motive force of batteries, 
365. 

Iron wire, 360. 

Metric weights and measures, 366, 
367. 

Relative conductivities, 365. 
Relative conductivity and resist¬ 
ance of metals, 364. 




376 


INDEX. 


Tables— 

Relative inductive capacity of in¬ 
sulators, 365. 

Relative resistance of liquids, 364. 
Weight and resistance of covered 
and bare copper wire, 363. 
Weight and resistance of galvan¬ 
ized iron wire, 362. 

Weights of insulated wire, 361. 
Tangent galvanometer, 101, 104. 
Tangents, 101. 

Telegraph, Morse American, 133, 

136. 

Alphabet, 356, 357. 

Arrangement of batteries, 136,144. 
Circuit arrangement of, 133. 

Key, 211, 213. 

Local circuit, 135. 

Proportionment of batteries, 145. 
Register, 215. 

Relay, 206, 209. 

Repeaters, 218, 221. 

Setting up instruments, 196. 
Sounder, 214. 

Telegraph lines, construction of, 153. 
Covered wires for, 183. 

Poles, 153, 155. 

Telegraph offices, hints for care of, 
229. 

Telegraphic circuits, 130. 

Faults in, 231, 233. 

Loops, 201. 

Systems still in use, 132. 

Testing for faults in, 233, 241. 
Telegraphs, early experimental, 131. 
District or messenger-call systems, 

137. 

Fire-alarm, 136. 

Operated by make and break of 
circuit, 140. 

Operated by reversals, 140. 

Police, 139. 

Stock-reporting, 139, 141. 
Type-printing instruments, 140, 
141. 

Multiple, 242. 

Duplex, 242, 250. 


Telegraphs— 

Electro-harmonic, 254, 265. 
Quadruplex, 250, 254. 

Telephone, the, 299. 

Ader, 304. 

Battery telephones, 304. 

Blake, 307. 

Construction of, 316. 

Crossley’s transmitter, 311. 

Crown, 303. 

Definition of word, 299. 

Dolbear’s receiver, 314. 

Edison transmitter, 306. 
Hunnings’s form, 313. 
Induction-coils for, 309, 351, 352. 
Magneto-telephone, 299. 

Operation of as transmitters 305. 
Patents, 351. 

Pony crown, 303. 

Standard Bell telephone, 302. 
Strength of current generated by, 
353. 

Telephone switch, 315. 

Uses of, 316, 317. 

Telephone lines, uninsulated, 183. 
Aerial cables for, 181, 183. 

Signals for, 297. 

Wire adapted for, 169. 

Telephone switches, 200. 

Telephonic communication through 
submarine cables, 190. 

Testing for circuit faults, 233, 241. 
For cross, 239. 

For defective ground terminal, 240. 
For disconnection, 233, 235. 

For escape, 238. 

For ground, 237. 

For intermittent disconnection, 
235. 

For intermittent ground, or cross, 
239. 

For partial disconnection, 236. 

For weather-cross, 240. 
Thermo-electric battery, 37, 39. 

Applications of, 39, 40. 
Thermo-electricity, 20, 36. 
Discovered by Seebeck, 36. 



INDEX. 


377 


Thomson’s reflecting galvanometer, 
107, 110. 

Time-balls and guns, electrically 
operated, 328. 

Underground lines, 184. 

Adaptation to telephony, 185,188. 
Electro-static capacity of, 353. 
First laid, 184. 

Materials of conductors and in¬ 
sulators, 184. 

Retardation in, 188. 

Where laid, 185. 

Units, employed in electrical mea¬ 
surements, 93, 97. 

Of capacity, 9G. 

Of current, 95. 

Of electro-motive force, 94. 

Of quantity, 95. 

Of resistance, 94. 

Universal switch, 197. 

Vibrating electric bells, 287. 

Volt, definition of, 94. 

Volta invented electrophorus, 353. 
Voltaic cell, 23. 

Battery, 24. 

Voltaic electricity, 22. 

How it differs from frictional, 22. 


Volta’s pile, 26. 

Weather-cross, 233, 240. 

Western Union pin-switch, 198. 
Wheatstone bridge, 110. 

Description of, 110, 111. 
Explanation of principles involv¬ 
ed, 111. 

Method of using, 111, 112. 

When introduced, 110. 

Wire, to ascertain weight per mile 
from diameter, 174. 

For telephone lines, 169. 
Galvanized, 170. 

Killing process, 175. 

Mechanical and electrical tests 
for, 171, 174. 

Preferable sizes for long lines, 168. 
Reason for preferring large wire, 
168. 

Resistance, variation with tempe¬ 
rature, 174. 

Sizes chiefly used, 166. 

Used for land lines, 165. 

Wire for inside construction, 192. 

Arrangement of in offices, 192. 
Wire-gauge, 166, 168. 

Zincs, amalgamation of, 25. 





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